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Support for extensions using XUL/XPCOM or the Add-on SDK was removed in Firefox 57, released November 2017. As there is no supported version of Firefox enabling these technologies, this page will be removed by December 2020.
Add-ons using the techniques described in this document are considered a legacy technology in Firefox. Don't use these techniques to develop new add-ons. Use WebExtensions instead. If you maintain an add-on which uses the techniques described here, consider migrating it to use WebExtensions.
Starting from Firefox 53, no new legacy add-ons will be accepted on addons.mozilla.org (AMO) for desktop Firefox and Firefox for Android.
Starting from Firefox 57, only extensions developed using WebExtensions APIs will be supported on Desktop Firefox and Firefox for Android.
Even before Firefox 57, changes coming up in the Firefox platform will break many legacy extensions. These changes include multiprocess Firefox (e10s), sandboxing, and multiple content processes. Legacy extensions that are affected by these changes should migrate to use WebExtensions APIs if they can. See the "Compatibility Milestones" document for more information.
A wiki page containing resources, migration paths, office hours, and more, is available to help developers transition to the new technologies.
This is a quick list of useful code snippets (small code samples) available for developers of extensions for the various Mozilla applications. Many of these samples can also be used in XULRunner applications, as well as in actual Mozilla code itself.
These examples demonstrate how to accomplish basic tasks that might not be immediately obvious.
- Examples and demos from MDN articles
- A collection of examples and demos from articles.
- Window code
- Opening and manipulating windows
- Toolbar related code
- Sidebar related code
- Forms related code
- Code used to parse, write, manipulate, etc. XML
- File I/O
- Code used to read, write and process files
- Drag & Drop
- Code used to setup and handle drag and drop events
- Code used to display and process dialog boxes
- Alerts and Notifications
- Modal and non-modal ways to notify users
- Code used to read, write, and modify preferences
- JS XPCOM
- Running applications
- Code used to run other applications
- WHAT WG Canvas-related code
- Signing a XPI
- How to sign an XPI with PKI
- Delayed Execution
- Performing background operations.
- Miscellaneous useful code fragments
- HTML to DOM
- Using a hidden browser element to parse HTML to a window's DOM
- A library that implements a
- By default, the only possible standardized scripting language for HTML is ECMAScript. Hence, if you are going to use another scripting language you might expect that most of the browsers will not recognize it. Nevertheless, the increasing computational power of modern browsers together with the introduction of typed arrays in ECMAScript allow us, in theory, to build full virtual machines in pure ECMAScript. Therefore, it is also possible, in theory, to use ECMAScript for a smaller task: parsing exotic programming languages (i.e., creating compilers). This snippets shows a possible way to start from.
- Tabbed browser code (Firefox/SeaMonkey)
- Basic operations, such as page loading, with the tabbed browser, which is the heart of Mozilla's browser applications
- Reading, writing, modifying, and removing cookies
- Page Loading
- Code used to load pages, reload pages, and listen for page loads
- Interaction between privileged and non-privileged code
- How to communicate from extensions to websites and vice-versa.
- Downloading Files
- Code to download files, images, and to monitor download progress
- Password Manager
- Code used to read and write passwords to/from the integrated password manager
- Code used to read and write bookmarks
- General information and utilities
- SVG Animation
- SVG Interacting with Script
- Embedding SVG in HTML and XUL
- Using SVG to enhance HTML or XUL based markup
- HTML in XUL for Rich Tooltips
- Dynamically embed HTML into a XUL element to attain markup in a tooltip
- Label and description
- Special uses and line breaking examples
- Setup and manipulation of trees using XUL and JS
- Changing style of scrollbars. Applies to scrollbars in browser and iframe as well.
- Code used to enable form autocomplete in a browser
- Tips and tricks when using boxes as containers
- Removing and manipulating tabs in a tabbox
- Finding Window Handles (HWND) (Firefox)
- How to use Windows API calls to find various kinds of Mozilla window handles. Window handles can be used for IPC and Accessibility purposes.
- Using the Windows Registry with XPCOM
- How to read, write, modify, delete, enumerate, and watch registry keys and values.
The content at MozillaZine Example Code is slowly being moved here, but you can still find useful examples there for now.