Index

Found 153 pages:

# Page Tags and summary
1 Firefox Developer Tools Developing Mozilla, Guide, Tools, Web Development, Web Development:Tools, l10n:priority
Examine, edit, and debug HTML, CSS, and JavaScript on the desktop and on mobile
2 3D view HTML, Tools, Web Development, Web Development:Tools
When you click on the 3D view button, the page goes into 3D view mode; in this mode, you can see your page presented in a 3D view in which nested blocks of HTML are increasingly "tall," projecting outward from the bottom of the page. This view makes it easy to visualize the nesting of your content.
3 Add-ons
Developer tools that are not built into Firefox, but ship as separate add-ons.
4 DOM Inspector DOM, DOM:Tools, DOM_Inspector, Extensions, Extensions:Tools, Themes, Themes:Tools, Tools, Web Development, Web Development:Tools, XUL, XUL:Tools
The DOM Inspector (also known as DOMi) is a developer tool used to inspect, browse, and edit the Document Object Model of documents - usually web pages or XUL windows. The DOM hierarchy can be navigated using a two-paned window that allows a variety of different views on the document and all nodes within.
5 DOM Inspector FAQ DOM_Inspector
The File menu contains approaches which will allow you to inspect a document.
6 DOM Inspector internals Code, Source, Tools, internals, organisation, source
There are three main facets to DOM Inspector. The one you are likely to be most familiar with is its inspector.xul-based primary UI. This is the two-pane inspector that appears when Ctrl+Shift+I (or Cmd+Shift+I) is pressed from one of the applications for which DOM Inspector has explicit support (i.e., menuitems placed via overlay).
7 Introduction to DOM Inspector DOM_Inspector
The DOM Inspector is a Mozilla extension that you can access from the Tools > Web Development menu in SeaMonkey, or by selecting the DOM Inspector menu item from the Tools menu in Firefox and Thunderbird, or by using Ctrl/Cmd+Shift+I in either application. DOM Inspector is standalone; it supports all toolkit applications, and it's possible to embed it in your own XULRunner app. DOM Inspector can serve as a sanity check to verify the state of the DOM, or it can be used to manipulate the DOM by hand, if desired.
8 Adding a panel to the toolbox
How to write an add-on that adds a new tool to the toolbox.
9 Browser Console Browser, Debugging, Tools, Web Development, WebDevelopment:Tools, debugging
The Browser Console is like the Web Console, but applied to the whole browser rather than a single content tab.
10 Browser Toolbox Debug, Firefox, JavaScript
The Browser Toolbox enables you to debug add-ons and the browser's own JavaScript code rather than just web pages like the normal Toolbox.  The Browser Toolbox's context is the whole browser rather than just single page on a single tab.
11 CSS Coverage
CSS Coverage is a set of commands for Firefox Developer tools that help untangle messy CSS by pointing out the CSS that isn't "used", and indicating the parts of your CSS files that are needed for initial rendering.
12 Contributing
This is a guide to contributing to the Firefox Developer Tools. At a high level, the workflow for a contributor looks like this:
13 Contribute on Nightly
This page describes a simple way of contributing to the Firefox Developer Tools that does not involve building Firefox or setting up any special environment.
14 DOM Property Viewer DOM, Tools, Web Development
The DOM Property Viewer lets you inspect the properties of the DOM as an expandable tree structure, starting from the window object of the current page or the selected iframe.
15 Debugger Debugger, Debugging, Dev Tools, Firefox OS, Tools, debugging, l10n:priority
The JavaScript Debugger enables you to step through JavaScript code and examine or modify its state to help track down bugs.
16 How to
These articles describe how to use the debugger.
17 Access debugging in add-ons
The following items are accessible in the context of chrome://browser/content/debugger.xul (or, in version 23 beta, chrome://browser/content/devtools/debugger.xul):
18 Black box a source
In modern web development, we often rely on libraries like jQuery, Ember, or Angular, and 99% of the time we can safely assume that they “just work”. We don’t care about the internal implementation of these libraries: we treat them like a black box. However, a library’s abstraction leaks during debugging sessions when you are forced to step through its stack frames in order to reach your own code. With black boxing, you can tell the debugger to ignore the details of selected sources.
19 Break on a DOM event
If you're listening to a particular DOM event, you can tell the debugger to break when the event is triggered without having to track down the listener and set a breakpoint manually.
20 Debug eval sources
You can debug JavaScript code that is evaluated dynamically, either as a string passed to eval() or as a string passed to the Function constructor.
21 Disable breakpoints
To disable a breakpoint, uncheck the check box next to the breakpoint's entry in the Source list pane:
22 Examine, modify, and watch variables
When the code has stopped at a breakpoint, you can examine its state in the variables pane of the debugger:
23 Highlight and inspect DOM nodes
If you hover over a DOM node in the Variables pane, it will be highlighted in the page.
24 Open the debugger
To open the debugger press the menu button ( new fx menu ), press "Developer", then select "Debugger". Or use the keyboard shortcut:
25 Pretty-print a minified file
To pretty-print a file that has been minified, open the minified file and click the icon that contains a pair of braces:
26 Search and filter
To search for items inside the debugger, use the script filter in the toolbar:
27 Set a breakpoint JavaScript, Tools
The following are different ways to set a breakpoint within the JavaScript code in the debugger.
28 Set a conditional breakpoint
To set a conditional breakpoint, activate the context menu while on the line you want to break at in the source pane, and select "Add conditional breakpoint". Then enter the conditional expression in the popup that appears:
29 Step through code
When your code stops at a breakpoint, you can step through it using the four buttons on the left of the toolbar:
30 Use a source map
JavaScript sources are often combined and minified to make delivering them from the server more efficient. Increasingly, too, JavaScript running in a page is machine-generated, as when compiled from a language like CoffeeScript or TypeScript. By using source maps, the debugger can map the code being executed to the original source files, making debugging much, much easier.
31 Keyboard shortcuts
1. By default, on some Macs, the function key is remapped to use a special feature: for example, to change the screen brightness or the volume. See this guide to using these keys as standard function keys. To use a remapped key as a standard function key, hold the Function key down as well (so to open the Profiler, use Shift + Function + F5).
32 Settings
The Debugger has its own settings menu, which you can access from an icon in the toolbar:
33 UI Tour
This article is a quick tour of the main sections of the JavaScript Debugger's user interface. The UI is split into six main sections, which we'll cover one at a time:
34 Debugger-API
Mozilla’s JavaScript engine, SpiderMonkey, provides a debugging interface named Debugger which lets JavaScript code observe and manipulate the execution of other JavaScript code. Both Firefox’s built-in developer tools and the Firebug add-on use Debugger to implement their JavaScript debuggers. However, Debugger is quite general, and can be used to implement other kinds of tools like tracers, coverage analysis, patch-and-continue, and so on.
35 Debugger.Object
A Debugger.Object instance represents an object in the debuggee, providing reflection-oriented methods to inspect and modify its referent. The referent's properties do not appear directly as properties of the Debugger.Object instance; the debugger can access them only through methods like Debugger.Object.prototype.getOwnPropertyDescriptor and Debugger.Object.prototype.defineProperty, ensuring that the debugger will not inadvertently invoke the referent's getters and setters.
36 Tools/Debugger-API/Conventions
This page describes general conventions used in the Debugger API, and defines some terminology used throughout the specification.
37 Tools/Debugger-API/Debugger
When called as a constructor, the Debugger object creates a new Debugger instance.
38 Tools/Debugger-API/Debugger.Environment
A Debugger.Environment instance represents a lexical environment, associating names with variables. Each Debugger.Frame instance representing a debuggee frame has an associated environment object describing the variables in scope in that frame; and each Debugger.Object instance representing a debuggee function has an environment object representing the environment the function has closed over.
39 Tools/Debugger-API/Debugger.Frame
A Debugger.Frame instance represents a visible stack frame. Given a Debugger.Frame instance, you can find the script the frame is executing, walk the stack to older frames, find the lexical environment in which the execution is taking place, and so on.
40 Tools/Debugger-API/Debugger.Memory
The Debugger API can help tools observe the debuggee’s memory use in various ways:
41 Tools/Debugger-API/Debugger.Script
A Debugger.Script instance may refer to a sequence of bytecode in the debuggee or to a block of WebAssembly code. For the former, it is the Debugger API's presentation of a JSAPI JSScript object. The two cases are distinguished by their format property being "js" or "wasm".
42 Tools/Debugger-API/Debugger.Source
A Debugger.Source instance represents either a piece of JavaScript source code or the serialized text of a block of WebAssembly code. The two cases are distinguished by the latter having its introductionType property always being "wasm" and the former having its introductionType property never being "wasm".
43 Tools/Debugger-API/Tutorial-Debugger-Statement
This page shows how you can try out the Debugger API yourself using Firefox's Scratchpad. We use the API to evaluate an expression in the web page whenever it executes a JavaScript debugger; statement.
44 Tutorial: Show Allocations Per Call Path Debugger, Tools, Tutorial
This page shows how to use the Debugger API to show how many objects a web page allocates, sorted by the function call path that allocated them.
45 DevTools API DevTools
The DevTools API provides a way to register and access developer tools in Firefox.
46 DevToolsColors CSS
This chart lists colors and CSS variables as implemented in the dark theme and light theme for developer tools.
47 Developer Toolbar Firefox, Tools, Web Development:Tools
The Developer Toolbar gives you command-line access to a number of developer tools from within Firefox. It is a Graphical Command Line Interpreter that provides integrated help for its commands and displays rich output with the power and conciseness of a command line. It is also extensible: you can add your own local commands and even convert them into add-ons so that other people can install them too.
48 Building GCLI For Firefox Build instructions
Technical review completed.
49 Customization
The mozcmd format is a way to store GCLI commands for easy access. It is available to Firefox users by setting the devtools.commands.dir to point to a directory containing a number of files with the extension mozcmd.
50 Future
This section is about future extensibility, it does not document current functionality.

GCLI currently has 3 extension points:
51 Display security and privacy policies Firefox, GCLI, Tools, Web Development:Tools
The security command displays information about the security and privacy settings for a website. There are two security subcommands:
52 Scratchpad
Technical review completed.
53 Writing GCLI Commands
The documentation that comes with GCLI has a section on writing commands. The documentation that follows describes the GCLI support provided in Firefox.
54 Editor
The Editor is a code-editor component that can be embedded in your addons. All existing Firefox Developer Tools currently use this component. Under the hood, the Editor component is a thin wrapper around the CodeMirror open source editor.
55 Example add-ons
Use these examples to understand how to implement a DevTools add-on.
56 Eyedropper
The Eyedropper tool enables you to select colors in the current page. It works like a magnifying glass over the page, enabling you to select with pixel precision. Underneath the magnifying glass it shows the color value for the current pixel using whichever scheme you've selected in Settings > Inspector > Default color unit:
57 Firefox OS 1.1 Simulator Firefox OS, Guide, Tools
The Firefox OS Simulator add-on is a tool that enables you to test and debug your Firefox OS app on the desktop. The code-test-debug cycle is much faster with the simulator than with a real device, and of course, you don't need a real device in order to use it.
58 Firefox OS Simulator
The Firefox OS Simulator is a version of the higher layers of Firefox OS that simulates a Firefox OS device, but runs on the desktop. This means that in many cases, you don't need a real device to test and debug your app. It runs in a window the same size as a Firefox OS device, includes the Firefox OS user interface and built-in apps, and simulates many of the Firefox OS device APIs.
59 Index Tools
Found 153 pages:
60 JSON viewer
Starting in Firefox 44, the Developer Edition includes a JSON viewer.
61 Keyboard shortcuts Tools, l10n:priority
This page lists all keyboard shortcuts used by the developer tools built into Firefox.
62 Memory DevTools, Firefox, Mozilla, Tools
The Memory tool lets you take a snapshot of the current tab's memory heap. It then provides a number of views of the heap that can show you which objects account for memory usage and exactly where in your code you are allocating memory.
63 Aggregate view
Before Firefox 48, this was the default view of a heap snapshot. After Firefox 48, the default view is the Tree map view, and you can switch to the Aggregate view using the dropdown labeled "View:":
64 Basic operations
The Memory tool is not enabled by default. To enable it, open the developer tool settings, and check the "Memory" box under "Default Firefox Developer Tools":
65 DOM allocation example
This article describes a very simple web page that we'll use to illustrate some features of the Memory tool.
66 Dominators
With a garbage-collected language, like JavaScript, the programmer doesn't generally have to worry about deallocating memory. They can just create and use objects, and when the objects are no longer needed, the runtime takes care of cleaning up, and frees the memory the objects occupied.
67 Dominators view
Starting in Firefox 46, the Memory tool includes a new view called the Dominators view. This is useful for understanding the "retained size" of objects allocated by your site: that is, the size of the objects themselves plus the size of the objects that they keep alive through references.
68 Monster example
This article describes a very simple web page that we'll use to illustrate some features of the Memory tool.
69 Tree map view
The Tree map view provides a visual representation of the snapshot, that helps you quickly get an idea of which objects are using the most memory.
70 Network Monitor Debugging, Dev Tools, Firefox, Guide, Networking, Tools, debugging, l10n:priority
The Network Monitor shows you all the network requests Firefox makes (for example, when it loads a page, or due to XMLHttpRequests), how long each request takes, and details of each request.
71 Page Inspector CSS, DOM, HTML, Stylesheets, Tools, Web Development, Web Development:Tools, l10n:priority
Use the Page Inspector to examine and modify the HTML and CSS of a page.
72 How to
Links for various HOW TO's can be found here. These links describe in depth the HOW TO techniques.
73 Edit CSS filters CSS, DevTools, Filters, Page Inspector, Tools
filter properties in the Rules view have a circular gray and white swatch next to them:
74 Examine and edit CSS Guide, Inspector, Tools
You can examine and edit CSS in the Inspector's CSS pane.
75 Examine and edit HTML Guide, Inspector, Tools
You can examine and edit the page's HTML in the HTML pane.
76 Examine and edit the box model Guide, Tools
With the Select Element button pressed, if you hover over an element in the page, the box model for the element is shown overlaid on the page:
77 Examine event listeners Guide, Inspector, Tools
From Firefox 33 you'll see an "ev" icon in the HTML Pane, next to elements that have event listeners bound to them:
78 Inspect and select colors Guide, Inspector, Tools
In the CSS Pane's Rules view, if a rule contains a color value, you'll see a sample of the color next to the value:
79 Open the Inspector Guide, Inspector, Tools
There are two main ways to open the Inspector:
80 Reposition elements in the page
Starting in Firefox 48 you can move absolutely positioned elements by dragging them around the page.
81 Select an element Guide, Inspector, Tools
If you opened the Inspector by clicking "Inspect Element", then an element will already be selected.
82 Use the Inspector API Inspector, Reference, Référence, Tools
Firefox add-ons may access the following objects from the chrome://browser/content/devtools/inspector/inspector.xul context:
83 Use the Inspector from the Web Console Guide, Inspector, Tools
The element that's currently selected in the Page Inspector can be referenced in the Web Console using the variable $0.
84 View background images
In the Rules view, you can see a preview of images specified using background-image. Just hover over the rule:
85 View fonts Guide, Inspector, Tools
If you hover over a font-family property in the Rules view, you will get a tooltip with a sample of that font:
86 Visualize transforms Guide, Inspector, Tools
If you hover over a transform property in the Rules view, you'll see the transformation overlaid in the page:
87 Work with animations Guide, Inspector, Tools
This article covers three tools you can use to visualize and edit animations:
88 Animation inspector (Firefox 41 and 42)
In Firefox 41 and 42, the Animation inspector enables you to:
89 Animation inspector example: CSS transitions
Example animation using CSS transitions.
90 Animation inspector example: Web Animations API
Example animation using the Web Animations API.
91 Keyboard shortcuts
These shortcuts work while you're in the Inspector's HTML pane.
92 UI Tour Guide, Inspector, Tools
This article is a quick tour of the main sections of the Page Inspector's user interface.
93 Paint Flashing Tool
The paint flashing tool, when activated, highlights the part of a page that the browser needs to repaint in response to some input: for example, the user moving the mouse or scrolling. With the help of this tool you can figure out whether your website is causing the browser to repaint more than it needs to. Because repaints can be performance-intensive operations, eliminating unnecessary repaints can improve your website's responsiveness.
94 Performance
The Performance tool gives you insight into your site's general responsiveness, JavaScript and layout performance. With the Performance tool you create a recording, or profile, of your site over a period of time. The tool then shows you an overview of the things the browser was doing to render your site over the profile, and a graph of the frame rate over the profile.
95 Allocations
To enable the Allocations view, you must check "Record Allocations" in the Performance tool settings, before recording a profile. Then record a profile as usual, and you will see a new tab labeled "Allocations" in the toolbar:
96 Call Tree JavaScript, Performance, memory, performance
The Call Tree is a sampling profiler. It periodically samples the state of the JavaScript engine and records the stack for the code executing at the time. Statistically, the number of samples taken in which we were executing a particular function corresponds to the amount of time the browser spent executing it.
97 Examples
List of demo pages for performance scenarios and walkthroughs.
98 Sorting algorithms comparison
This article describes a simple example program that we use in two of the Performance guides: the guide to the Call Tree and the guide to the Flame Chart.
99 Flame Chart
The Call Tree and the Flame Chart are both used to analyze your site's JavaScript, and they both use the same data: a sample of the JavaScript engine's stack, taken periodically during the recording.
100 Frame rate
Frame rate is the rate at which a video device can produce images (or frames). It's most familiar from film and gaming, but is now widely used as a performance measure for websites and web apps.
101 How to
To open the Performance tools:
102 Scenarios NeedsContent
Performance scenarios
103 Animating CSS properties
With CSS animations you specify a number of keyframes, each of which uses CSS to define the appearance of the element at a particular stage of the animation. The browser creates the animation as a transition from each keyframe to the next.
104 Intensive JavaScript
If you want to play along you can find the demo website here.
105 UI Tour
The performance tool's UI consists of 4 main pieces:
106 Waterfall
107 Release notes
Highlights:
108 Remote Debugging Tools, l10n:priority
You can use the Firefox developer tools on your desktop to debug Web sites and Web apps running in other browsers or runtimes. The other browser might be on the same device as the tools themselves or on a different device, such as a phone connected over USB.
109 Debugging Firefox Desktop Debugging, Guide, Tools
This guide explains how you can use the Firefox Developer Tools to debug a different instance of desktop Firefox running on the same machine. In this guide, the instance of Firefox being debugged is called the debuggee, and the instance of Firefox doing the debugging is called the debugger.
110 Debugging Firefox OS over USB
This guide explains how to connect the Firefox Developer Tools to a Firefox OS device over USB.
111 Debugging Firefox OS over WiFi
This article describes how to connect the Firefox Developer Tools to a Firefox OS device over WiFi.
112 Debugging Firefox for Android over USB remoteDebug
This article describes how to connect the Firefox Developer Tools to Firefox for Android from Firefox 36 onwards. For connecting over WiFi, see corresponding page.
113 Debugging Firefox for Android over WiFi
Technical review completed. Editorial review completed.
114 Debugging Firefox for Android with WebIDE Debugging, Guide, Tools
This article describes how to connect the Firefox Developer Tools to Firefox for Android from Firefox 36 onwards.
115 Remotely debugging Chrome Desktop
How to connect the Firefox Developer Tools to the Google Chrome browser running on the desktop.
116 Remotely debugging Firefox <36 for Android Android, Debugging, android, debugging
This guide explains how to use remote debugging to inspect or debug code running in Firefox for Android over USB.
117 Remotely debugging Firefox for Metro
This article explains how to use remote debugging to inspect and code running in the new Windows 8 ("Metro-style") Firefox app, using the developer tools in Firefox on the desktop.
118 Remotely debugging Thunderbird Debug, Tutorial, thunderbird
This guide explains how to use remote debugging to inspect or debug code running in Thunderbird.
119 Responsive Design Mode Design, Dev Tools, Firefox, Guide, Responsive Design, Tools, Web Development, l10n:priority
Responsive designs adapt to different screen sizes to provide a presentation that is suitable for different kinds of devices, such as mobile phones or tablets. Responsive Design Mode makes it easy to see how your website or web app will look on different screen sizes.
120 Rulers
New in Firefox 40.
121 Scratchpad Scratchpad, Tools, Web Development, Web Development:Tools, l10n:priority
Scratchpad provides an environment for experimenting with JavaScript code. You can write, run, and examine the results of code that interacts with the web page.
122 Settings
To see the Developer Tools Settings pane, open any of the Developer Tools, and then:
123 Shader Editor
The Shader Editor enables you to see and edit the vertex and fragment shaders used by WebGL.
124 Storage Inspector Cookies, Dev Tools, Firefox, Guide, IndexedDB, Local Storage, Session Storage, Storage, Tools, cookies, storage
The Storage Inspector enables you to inspect various types of storage that a web page can use. Currently it can be used to inspect the following storage types:
125 Style Editor CSS, Stylesheets, Tools, Web Development, Web Development:Tools
The Style Editor enables you to:
126 The Web Developer Menu Add-ons, Debugging, Tools, Web Developer
The Web Developer menu is the main way to access the developer tools that are built into Firefox. On OS X and Linux, it's under the "Tools" menu:
127 Toolbox
The Toolbox provides a single home for most of the developer tools that are built into Firefox.
128 Tools/Debugger.Object
A Debugger.Object instance represents an object in the debuggee, providing reflection-oriented methods to inspect and modify its referent. The referent's properties do not appear directly as properties of the Debugger.Object instance; the debugger can access them only through methods like Debugger.Object.prototype.getOwnPropertyDescriptor and Debugger.Object.prototype.defineProperty, ensuring that the debugger will not inadvertently invoke the referent's getters and setters.
129 Valence (Firefox Tools Adapter)
Valence (formerly Firefox Tools Adapter) is an experimental add-on that enables the Firefox Developer Tools to debug a wider variety of browsers, not just the Gecko-based Firefox, Firefox for Android, and Firefox OS browsers.
130 Validators Tools, Website validator, html5 validator, validator
This document lists different resources for developers to validate web pages.
131 View Source
View Source lets you look at the HTML or XML source for the page you're viewing. To activate View Source:
132 Web Audio Editor Tools
With the Web Audio API, developers create an audio context. Within that context they then construct a number of audio nodes, including:
133 Web Console Debugging, Guide, Security, Tools, Web Development, Web Development:Tools, debugging, l10n:priority, web console
The Web Console:
134 Console messages
Most of the Web Console is occupied by the message display pane:
135 Custom output in the Web Console Extensions, Guide, Reference, Référence, web console
This document describes how you can extend and customize the output of the Web Console and of the Browser Console. Here you can also learn how to extend the object previews we generate in the consoles and in the Object Inspector.
136 Keyboard shortcuts
These shortcuts apply when you're in the command line interpreter.
137 Opening the Web Console
To open the Web Console:
138 Rich output
When the Web console prints objects, it includes a richer set of information than just the object's name. In particular, it:
139 Split console
You can use the console alongside other tools. While you're in another tool in the Toolbox, just press Esc or press the "Toggle split console" button in the Toolbar. The toolbox will now appear split, with the original tool above and the web console underneath.
140 The command line interpreter
You can interpret JavaScript expressions in real time using the command line provided by the Web Console.
141 Web Console Helpers Debugging, Web Development, debugging, web console
The JavaScript command line provided by the Web Console offers a few built-in helper functions that make certain tasks easier.
142 Web Console remoting Debugging, Reference, Référence, web console
This document describes the way Web Console remoting works. The Web Console is split between a client with its user interface, and the server which has listeners for all the things that happen in the tab. For communication between the server and the client we use the Remote Debugging Protocol. This architecture allows you to connect a Web Console client instance to a server running on B2G, Fennec or some other Firefox instance.
143 WebIDE Apps, B2G, Debugging, Firefox OS, WebIDE, WebIde, debugging, tool
With WebIDE, you first set up one or more runtimes. A runtime is an environment in which you'll run and debug the app. A runtime could be a Firefox OS device connected to the desktop over USB (or over Wi-Fi since Firefox 39), or it could be a Firefox OS Simulator installed on the desktop itself.
144 Creating and editing apps
The sidebar on the left-hand side of the WebIDE enables you to:
145 Monitor
The WebIDE Monitor
146 Opening WebIDE WebIDE, WebIde, opening
There are three ways to open WebIDE:
147 Running and debugging apps
When you're ready to run the app, you need to select a runtime from the Runtimes sidebar. If you don't have any available runtimes here, find out how to add some in Setting up runtimes.
148 Setting up runtimes
A runtime is an environment in which you'll run and debug the app, such as a web browser. A runtime could be:
149 The runtime menu
Once you've selected a runtime, you can access the runtime settings:
150 WebIDE Troubleshooting
If you're trying to connect a Firefox OS device to WebIDE and it doesn't show up, here are some things you can try:
151 Working with Cordova apps in WebIDE
Technical review completed. Editorial review completed.
152 Working with iframes Debugging, DevTools, Developer Tools, Frames, Tools
From Firefox 34 onwards, you can point the developer tools at a specific iframe within a document.
153 about:debugging
The about:debugging page provides a single place from which you can attach the Firefox Developer Tools to a number of debugging targets. At the moment it supports two main sorts of targets: restartless add-ons and workers.

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 Contributors to this page: fscholz
 Last updated by: fscholz,