Firefox Headlines (October 21st, 2021)

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Amy Churchwell

Oct 21, 2021, 2:18:24 PM10/21/21

Howdy Firefox friends! 🔥🦊

Here is a belated (apologies!) update from the Firefox Desktop team from our previous meeting! Every two weeks the Firefox Desktop engineering teams get together to discuss the various goings-on in the codebase. Here is a condensed version for your reading pleasure:


Friends of the Firefox team
Fixed more than one bug

  • Itiel

Project Updates

Add-ons / Web Extensions

Addon Manager & about:addons

  • Fixed a bug related to the addon descriptions not being localized as expected when switching the browser to a different locale - Bug 1712024

  • Introduced a new “extensions.logging.productaddons.level” about:config pref to control log level related to GMP updates independently from the general AddonManager/XPIProvider logging level - Bug 1733670  

WebExtensions Framework

WebExtension APIs

  • Starting from Firefox 94, a new partitionKey property is being introduced in the cookies API, this new property is meant to help extensions to better handle cookies partitioned by the dFPI feature

Downloads Panel

  • Many tests being addressed and fixed with improvements pref enabled (ticket)

  • [kpatenio] New context menu item being worked on for new pref (ticket)


  • The Fission experiment on Release has concluded, and the data science team is now analyzing the data. So far, nothing has jumped out to us showing stability or performance issues.

  • Barring any serious issues in the data analysis, the plan is to slowly rollout Fission to more release channel users in subsequent releases.


Password Manager 


  • dthayer landed a fix that improves scaling of iframes with Fission enabled

  • mconley helped harry find a solution for a white flash that can occur when a theme is applied to about:home during the first boot

  • Special shout-out to zombie from the WebExtensions team for helping to reduce Base Content JS memory usage by 3-4% on all desktop platforms!

  • We’re starting to get numbers back on how the Fluent migrations have been impacting startup:

    • There appears to be evidence that the localization cycle for the first window is ~32% faster for the 95th percentile of users on Nightly, and ~12% faster for the 75th percentile.

    • Subsequent new windows see localization cycle improvements of ~12% for the 95th percentile

    • TL;DR: Removing DTDs from the main windows has improved startup time and new window opening for some of the slowest machines in our user pool.

Performance Tools

  • Isolated web content processes now display eTLD+1 of their origin in the Firefox Profiler timeline when Fission is enabled.

  • Gecko profiler Rust marker API has landed. It’s possible to add a profiler marker from the Rust to annotate a part of the code now. See the gecko-profiler crate for more information. Documentation is also coming soon.

Search and Navigation

  • Daisuke has replaced the DDG icon with one having better quality. Bug 1731538 

  • Thanks to Antonin Loubiere for contributing a patch to make ESC actually undo changes in the separate search bar, instead of doing nothing, more similarly to how the address bar behaves. Bug 350079 


  • Thanks again to module owner Emma whose last day was Friday. Sam Foster will take over as module owner. 

  • niklas working on bug 1714234 that fixes screenshot test issues when copying image to clipboard.

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