Contained in the Firefox OS Settings app is the Developer panel. This panel offers a number of options that can make debugging your open web app on Firefox OS easier. This article covers the options available and how to make use of them.
The settings panel for developer options is intentionally buried deep to avoid having end users who have no need for these options inadvertently turning on options that make their device run more slowly or add strange visual effects to their displays. The panel looks something like this (the following is from a Geeksphone Keon running an April 2014 build of Firefox OS 2.0; yours may differ if you are running a different version):
The developer panel is reached as follows:
- In Firefox OS <1.4, you open the developer panel via Settings > Device information > More Information > Developer.
- In Firefox 1.4+, you have to enable the developer panel via Settings > Device information > More Information > Check the Developer Menu checkbox. Once you've done this, you can then access the developer panel via Settings > Developer.
The following sections cover each of the options in the Developer panel, explaining what they do and why they're useful.
Developer Tools settings
Debugging via USB
The "Remote debugging" option enables support for remotely debugging your Firefox OS device. This also enables ADB command usage. In Firefox <1.4 there is only a single checkbox; in Firefox 1.4 there are three options available in a select box:
- Disabled: remote debugging is turned off (the default.)
- ADB only: Allows access to the device by ADB.
- ADB and Devtools: Allows access to the device by ADB and Firefox Devtools such as the App Manager.
In Firefox OS 1.4+, tapping this section brings you to the Developer HUD selection view.
There's a checkbox you can use to enable or disable the Developer HUD altogether (a section at the top of the Firefox OS UI for displaying developer information), and then five checkboxes to enable or disable:
- Log changes in adb: Enables logging of device changes to adb logcat.
- Warnings: Displays console warnings.
- Errors: Displays console errors.
- Security issues: Displays potential security issues.
- Reflows: Displays reflows as they occur.
- Jank/Jank threshold: Notify the phone user about occurrences of unacceptably high jank, the threshold for which can be customised.
- Frames per second: Displays frames per second, as explained in the Frames_per_second section below.
- Time to load: Displays time to load information, as explained in the Time_to_load section below.
- App memory: Displays information on how much memory the app is using, and allows you to enable or disable the different memory usage factors. See App_memory below for more details.
Frames per second
Enabling this option reports three numbers in the top left of the Firefox OS display; the values reported are an average of recent results within a sliding window, meant to be "instantaneous" but fairly accurate. As such, all numbers are "guesses":
- The left number is the composition rate: the estimated number of times per second Firefox OS is drawing frames to the hardware framebuffer. This is an estimate of the user-perceived framerate, and only an estimate. For example, the counter may report 60 compositions per second even if the screen is not changing. In that case the user-perceived framerate would be 0. However, when used with this caveat in mind and corroborated with other measurements, the monitor can be a useful and simple tool.
- The middle number is the layer transaction rate, the estimated number of times per second processes are repainting and notifying the compositor. This number is mostly useful for Gecko platform engineers, but it should be less than or equal to the composition rate number on the left.
- The right hand number is a measure of the number of pixels drawn as a percentage of the screen size. A number of 273 means the screen was painted 2.73 times. Ideally this number should be as close to 100 as possible.
Time to load
Firefox OS also has a tool that can help measure startup time, specifically the "first paint" time. The value shown by the tool — in the top right of the Firefox OS display — is the elapsed time between when the most recent application was launched, and an estimate of the first time that application painted its UI, in milliseconds. This number only approximates the real "first paint" time, and in particular underestimates it. However, lowering this number almost always correlates to improvements in real startup time, so it can be useful to quickly measure optimization ideas.
Displays information on how much memory the app is using, and allows you to enable or disable the different items that use memory to show much each one is using in the current app. For example, the screen shot below only has App memory and JS objects checked, and the indicator on the bottom right is showing that the Settings app is using 414.77KB for JS objects.
Flash repainted area
In this mode, every time a region of the screen is painted by Gecko, Gecko blits a random translucent color over the painted region. Ideally, only parts of the screen that visually change between frames will "flash" with a new color. But sometimes more area than is needed is repainted, causing large areas to "flash". This symptom may indicate that application code is forcing too much of its scene to update. It may also indicate bugs in Gecko itself.
Enable APZ for all content (was Async Pan/Zoom)
When enabled, the Async Pan/Zoom module allows panning and zooming to be performed on asynchronously, on another thread, with some noticeable differences to rendering behaviour. To find out more, read the MozillaWiki APZ article.
Tiling (was Layers: Enable tiles)
Introduced in Firefox OS 1.4, this feature enables the painting of content to the screen in smaller chunks ("tiles") rather than painting the whole screen at once. This is mainly useful for platform QA work involving reducing checkerboarding and finding regression windows.
Simple tiling (was Layers: Simple tiles)
This flips between the two different content painting implementations described in the section above.
Hardware composer (was Enable hardware compositing)
When enabled, this setting causes the device to use its Hardware Composer to composite visual elements (surfaces) to the screen.
Draw tile borders (was Layers: Draw tile borders)
This is very similar to the Draw layer borders option, the difference being that it also draws the borders for individual tiles as well as the borders around layers.
Draw layer borders
When this setting is enabled, a brightly colored border is added around all the different layers painted to the display — great for diagnosing layout issues.
Dump layers tree
This option causes a copy of the compositor's layer tree to be dumped to logcat on every frame composited to the screen; this is mainly useful for platform graphics performance work, rather than regular web development.
Cards View: Screenshots
When enabled, this specifies that app screenshots will be taken when the open apps are displayed in card view. If disabled, app icons are shown in the center of blank cards for the card view instead.
Window management settings
Software home button
Enabling this option creates a software home button that can provide the same functionality as the equivalent hardware button if it is not available. This is intended for future use on devices that are likely to not have hardware home buttons, like tablets.
Enabling this option allows you to swipe upwards towards the center from outside the screen to bring up the homescreen. Again, this can provide the same functionality as the equivalent hardware button if it is not available, and is intended for future use on devices that are likely to not have hardware home buttons, like tablets.
Enabling this option allows you to swipe left and right from outside the screen towards the center, to navigate to the next and previous sheets (either web pages in the browser, or views inside another app.) This basically works like the browser navigator bar in Firefox.
This setting allows you to decide whether app keyboards open immediately or continuously (with a transition). Disabling such transition effects are useful on low end devices, when they cause performance to suffer.
Turn this on and then off again and you will disable all app closing/opening transitions: all apps will now just show immediately, without the smooth animation, and keyboards will also open/close without animation. Like "Continuous transition enabled", this is meant for improving performance on low end devices, but it has more of an effect.
If enabled, this specifies that when an app is killed in the background, it will be kept in history and reopened when you open it from homescreen/card view. If disabled, such apps are not kept in history/card view.
Log slow animations
This tool tries to help developers understand why animations are not offloaded to the compositor to be run efficiently as possible. It reports "bugs" like trying to animate elements that are too large, or trying to animate CSS properties that can't be offloaded. The messages you'll get on the device will look like the following:
I/Gecko ( 5644): Performance warning: Async animation disabled because frame size (1280, 410) is bigger than the viewport (360, 518) [div with id 'views']
Wi-Fi output in adb
Enabling this option adds information about Wi-Fi to the adb logs (error logs from the console can be accessed using
adb logcat | grep "Error" in the Terminal.)
Bluetooth output in adb
Enabling this option adds information about Bluetooth to the adb logs (error logs from the console can be accessed using
adb logcat | grep "Error" in the Terminal.)
Gaia debug traces
Enabling this directly enables DEBUG traces in Gaia; see bug 881672 for more details.
Note: Unfortunately, not every app supports this mechanism to print their debug log. Instead, they control a "DEBUG" flag in code directly, so enabling this flag does NOT ensure that you'll see all debug logs.
Show accessibility settings
This enables the accessibility settings menu, subsequently found at Settings > Accessibility. The options contained within are as follows:
Enabling this option turns on Firefox OS's screen reader. Currently at a very early stage, it changes the way the standard touch events work. For example, you can:
- Long press somewhere to focus that app (or whatever) and be alerted as to what it is, then double click to select it.
- Swipe from top to bottom to do a "tab" equivalent, moving sequentially through apps and being alerted to each one's name.
- Swipe from bottom to top to do "shift tab", moving sequentially backwards through apps and being alerted to each one's name.
A slider that controls how loud the speech is delivered.
A slider that controls how fast the speech is delivered.
Launch first time use
The "Launch first time use" button runs the first-time startup program; this lets you go through the initial setup and tutorial process, and is useful when trying to debug that process, or if you want to re-configure your device from scratch.
This section lists settings that are no longer provided, or no longer exist in the same state, but might still be interesting if you are running an older version of Firefox OS.
In versions of Firefox earlier than newer 1.4 versions, this controls the accessibility settings, as explained in the Show_accessibility_settings section above.
The "Grid" option, when enabled, causes the Firefox OS display to be overlaid with a grid pattern to help you gauge positioning and alignment of items. For example, below we see the Browser app running with the Grid option enabled:
The grid's heavier lines are 32 pixels apart, both horizontally and vertically.
Show frames per second
In Firefox OS versions older than newer 1.4, enabling this displays frames per second, as explained in the Frames_per_second section above.
Show time to load
In Firefox OS versions older than newer 1.4, enabling this displays time to load information, as explained in the Time_to_load section above.
In Firefox OS versions older than newer 1.4, this option enables the new Firefox Rocketbar on your device, which provides a useful new way to switch between apps, search, and more. When enabled, you'll find a search icon at the top left of the device, and the RocketBar can be brought up by swiping from the top left of the device towards the bottom left.
Note: In newer versions of Firefox OS, Rocketbar is enabled automatically and cannot be turned off.
Contacts debugging output in adb
Enabling this option adds debugging information about contacts to the adb logs (error logs from the console can be accessed using
adb logcat | grep "Error" in the Terminal.)
Progressive paint (was Layers: Progressive paint)
This was introduced to help with debugging of the Async Panning/Zoom module (APZ) during its implementation. Now APZ implementation is complete, this option is deprecated, and will be removed from future versions (see bug 1003228).
- Center displayport
- Assume perfect paints
- Taller displayport
- Faster paints
- No checkerboarding
These options were introduced to help with debugging of the Async Panning/Zoom module (APZ) during its implementation, specifically to allow QA to experiment with different repainting heuristics to see which resulted in the least amount of checkboarding.. Now APZ implementation is complete, these options are deprecated, and will be removed from future versions (see bug 1003228).
In addition to the developer-specific options listed above, Firefox OS < 1.4's developer settings featured keyboard layout options. These let you toggle on and off the then-experimental Chinese input methods:
As of Firefox 1.4, these options have been removed. This is because the Chinese keyboard layout implementations (zhuyin and pinyin) have now been completed.
Note: For other keyboard layouts still under development, such as Japanese, we now have a build-time config to opt them in.