Firefox Headlines (September 23rd, 2021)

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Emma Malysz

Sep 23, 2021, 6:39:22 PM9/23/21
Hey Firefox friends!

The Firefox Desktop team met this week to share notes and updates on some of the great things we've been working on. Here's a condensed and organized set of notes for you to enjoy!

Thanks to Sam Foster, Harry Twyford, Mike Conley, Yasmin Shash, Katherine Patenio, and Niklas Baumgardner who helped me put these together.


  • We have begun to roll out fission to a fraction of users on the release channel! Here’s a reminder of what Fission is, and why it matters

    • Telemetry so far doesn’t show any problems with stability or performance. We’re keeping an eye on it.

  • Fluent milestone 1 is 100% completed! All DTDs have been removed from browser.xhtml!

    • [Screenshot]

      • Caption: A burndown chart for strings in browser.xhtml. No remaining DTDs left.

  • A new group of students from Michigan State University are working on improvements to High Contrast Mode. See the High Contrast Mode section below for details. Thanks to Noah, Shao, Danielle, Avi, and Jack!

  • about:processes is a page that you can go to to see which Firefox processes are taking up power and memory on your machine

    • It’s now possible to record a performance profile for a process with only a single click from within about:processes!

    • Here’s an animated GIF demonstrating a example workflow of one-click profiling

  • The new tab redesign has officially graduated. The pref to enable the pre-89 design has been removed.

  • Experimental improvements to macOS video power consumption will land soon in bug 1653417.

    • Fullscreen Youtube video on macOS consumes only 80% of the power it otherwise would.

    • We’re looking for testers! Flip gfx.core-animation.specialize-video to test. We’re looking specifically for visual glitches in the video or its controls. We’d also like to confirm that power usage is reduced for fullscreen YouTube and Twitch videos.

Friends of the Firefox team


  • [mconley] Welcome Yasmin Shash and Hanna Jones!

  • [vchin] Welcome to Amir who has started as Desktop Integrations EM!

For contributions from September 8th to September 21st 2021, inclusive.

Resolved bugs (excluding employees)

Fixed more than one bug

  • Antonin Loubiere

  • Itiel

New contributors (🌟 = first patch)

Project Updates

Add-ons / Web Extensions

WebExtensions Framework

Downloads Panel


  • Milestone 1 has been completed! All DTDs have been removed from browser.xhtml!

    • As a bonus, this also means that all DTDs have been removed from the startup path, which was a goal for Milestone 2!

    • Are We Fluent Yet?

    • Congratulations to Katherine and Niklas for finally getting us over this milestone!

Form Autofill

High-Contrast Mode (MSU Capstone project)

Lint, Docs and Workflow

macOS Spotlight

  • Window spotlight buttons will now be on the correct side in RTL builds: bugs 1633860 & 1419375.

  • We noticed some users unfamiliar with macOS conventions were running Firefox directly from its DMG file. This can result in data loss and slow startup times, since Firefox is not fully installed. We now show a message warning the user in this scenario (bug 516362).

New Tab Page

  • New tab redesign has officially graduated. Old design pref & related code removed. Bug 1710937 👏

  • CSS variables simplified & cleanup. Allowing for easier theming (bug 1727319, 1726432, 1727321)

  • The ntp_text theme API property was broken, and now it isn’t! (bug 1713778)

Nimbus / Experiments

  • Bug 1730924 We want to update the Ajv JSON schema validator in tree

Password Manager

PDFs & Printing 


  • Gijs has filed some bugs to make process flipping less likely when Fission is enabled

  • We’ve been seeing a slow but steady decline in the percentage of clients on Nightly seeing tab switch spinners. This might be related to Fission, WebRender, hardware churn, or might be a measurement artifact due to old builds sending telemetry. We’re not sure.

  • Thanks to jstutte for landing a patch that removes some main thread IO during startup when checking if we need to be doing an LMDB migration!

Performance Tools

  • Thanks to our contributor, mhansen, Linux perf profiles now include different colors for kernel vs user stack frames.

    • [Screenshot]

      • Caption: Two side-by-side images of performance profiles. The right side now has bright colors


Search and Navigation

  • Firefox Suggest is a new feature we’re working on to help you find the best of the web more quickly and easily!

  • Drew enabled the Firefox Suggest offline scenario for en-* users in the US region and made some tweaks to the Address Bar preferences UI

  • Daisuke fixed a regression where the Address Bar was not providing switch-tab results when history results were disabled - Bug 1477895 


Below the fold

  • [standard8] Please ensure your mentored bugs are up to date, and in a clear state for being picked up by potential contributors.

    • Please also take a look at the Firefox and Toolkit mentored bugs where the mentors have now left - are there any bugs you'd be willing to take over mentorship for, or that are just not relevant now?

    • Firefox-dev email

    • Thank you to those that have already looked.

  • [mconley] We have BrowserTestUtils.waitForMutationCondition, which is really handy for when you want to wait for the DOM to reach some state. Better than TestUtils.waitForCondition since it doesn’t depend on random polling.

  • [kpatenio] You can run startup profile selection menu with local build of firefox using the -P parameter, and that there’s a wiki

    • Example: `./mach run -P`

    • Also handy: `./mach run --profile /tmp/foo` or `./mach run --temp-profile` or `./mach run --temp-profile --setpref foo=true`

This information, including all of the previous updates, are fully available in this doc:

Also note that I'm really just synthesizing and humanizing the stuff that's on the Wiki, which is freely available from here:, so check that out if you want the source material. It'll also be posted (minus the Below the Fold stuff) to the Nightly blog.

Finally, if there's a Firefox-ish team that you feel isn't being represented here, please let them know about the above meeting so we can get their updates.

Keep on rockin' the free web,


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