Categories: News

These Weeks in Firefox: Issue 66


  • QuantumBar redesign, aka ‘MegaBar’
    • We’re hoping to be able to make Firefox 71, but it might become 72. This feature is now enabled in Nightly!
    • We already collected useful feedback and are working on the remaining problems; notably we made the animation smoother, thanks to running on mouseup and using CSS transforms only. It is also skipped when prefers-reduced-motion is true.
    • We introduced retained results: If you start to search, then click outside the bar and back in, the results are shown again.
  • In Firefox 71, we are removing the AppCache storage mechanism, so that we only have the JavaScript API remaining, which will also be removed soon.
    • If you’re still using AppCache, please stop. Please use ServiceWorkers instead.
  • You can now have a separate search engine in private browsing mode, which we intend to ship in Firefox 71. You can enable this on Nightly by setting the preference to true in about:config. Feel free to test in Nightly and report bugs as blocking Bug 1411340.
  • We’ve set up to track our progress on the Fission (out-of-process iframes) project. Right now, it’s showing our progress enabling mochitests with Fission enabled
  • Only one more XBL binding left! (here’s the bug for last binding, and our tracking dashboard)
    • This is an older, non-standard UI technology that we’ve been trying to get rid of for a while.

Friends of the Firefox team

Resolved bugs (excluding employees)

Fixed more than one bug

  • Chujun Lu
  • Florens Verschelde :fvsch
  • Jorg K (GMT+2)
  • Kestrel
  • mattheww
  • Miriam
  • Sorin Davidoi
  • Zhao Gang

New contributors (🌟 = first patch)

Project Updates

Add-ons / Web Extensions

  • Shane removed the remaining pieces of old proxy extensions API based on the PAC scripts, as we have announced the deprecation in Firefox 68 (Bug 1443259)
  • Tomislav added back the “install” site permission associated with the AMO website url, to prevent a “website trust warning” to be shown when installing an addon from AMO on a slow network (Bug 1560059)
  • First part of the changes needed to hand-off AMO abuse reports to Firefox integrated abuse report panel has been landed on central (Bug 1580554)
  • A content script CSS cleanup bug that was triggering (too many and not very useful) nsIDOMWindowUtils.removeSheet errors on every closed tab (Bug 1550470) has been finally fixed
  • Emilio fixed a bug that was preventing the addon icons to update as expected when Firefox is switched into Dark mode (Bug 1581117), and improved the way we use to notify Dark mode changes to the LightweightThemeConsumer.jsm (Bug 1583941)
  • Mark Banner fixed a bug in IgnoreLists.jsm that would prefer extension that overrides the homepage from installing successfully if the “hijack-blocklists” remote settings collection is in an invalid state (Bug 1585972)
  • Nils Maier (DownThemAll! author) contributed a fix for Bug 1296365, and so Firefox now shows the extension name and page title in the ‘extensions’ popup windows title (instead of the extension url). Thanks Nils for contributing this enhancement!!!

Browser Architecture

Developer Tools

  • The Inactive CSS feature is green on Beta, and is happily riding the trains to release. The latest validator we added is about properties that don’t work in :visited CSS rules.
  • The WebCompat issues extension we have been working on is now moving to its next stage: becoming a built-in inspector sidebar panel!
  • The new multi-line console editor mode is getting a new button to open the “reverse search” feature. This way you don’t even really miss the old scratchpad save/open feature since you can simply recall previous code snippets.

Screenshot of the dev-tools console showing the new button to open history reverse search.

  • Most of the team is busy with Fission-related work. Our first milestone is related to making the Browser Toolbox a better version of itself (we’re calling it the Omniscient Browser Toolbox) that shows a lot more stuff (parent process stuff, like before, and content process stuff too!). 🎉🎉🎉
  • We’ve also made great progress on RDM to stop using the <iframe mozbrowser> piece of technology that it is currently based upon. Although still too early to test, work is happening on this bug, below this pref: devtools.responsive.browserUI.enabled.



  • Non-ascii characters (e.g. ⏎ on prettier reports) will now be correctly displayed on treeherder summaries & logs. Thanks to Ahal for the python 3 switch.
  • We are starting to experiment with Type Safety in Javascript – with initial tests using TypeScript on some of the devtools code. See Mossop’s post on dev.platform for more details.

Mobile Browsers

  • Fennec (Firefox for Android) source is no longer part of mozilla-central: Bug 1580356.  Fennec continues to be shipped from mozilla-esr68.
  • Firefox Preview and Android Components are actively supporting contributors in GitHub’s Hacktober, a month-long event that encourages open-source contributions. See our blog post.

New Tab Page

  • New modal opened from Pocket card context menu to display ad privacy info.
  • Investigation around a rollout issue we had and an unexplainable ad blocking issue.

Password Manager

  • eTLD+1 (Subdomain) autocomplete
    • Working on this to get it ready to ride the trains. It has been on Nightly since All Hands.


Performance Tools

  • Recording of native allocation stacks is now possible to test. Enable it with the “Native Allocations” checkbox at the bottom of the Features list in the profiler capture panel. (Warning: start the profiler using the ‘Start recording’ button of the panel; the keyboard shortcut currently doesn’t take into account this new checkbox; we’ll fix this soon)
    Here is an example profile of opening 3 new browser windows

Screenshot of an example performance profile showing native allocation stacks in the graph.

  • No sampling mode has landed. This dramatically reduces profiler overhead by collecting only markers. It can currently be enabled for startup profiles with the nostacksampling feature name. It’s not visible yet in the profiler popup; we’ll be adding a checkbox for it soon.


  • Continue to be on track for releasing to users on Windows in Firefox 71. The plan is to do a slow rollout via Normandy.
  • We’re hoping to start on macOS and Linux support next.
  • Fixed
    • Bug 1549442 – Picture-in-Picture toggle does not collapse or disappear if the mouse moves outside of the window.
    • Bug 1581942 – Snapping Picture-In-Picture videos to the left/right/top with the keyboard displays thick white bars on the video’s sides
    • Bug 1582171 – [Amazon Prime] PiP window becomes white if the next episode is loaded
    • Bug 1582178 – [Amazon Prime] PiP window becomes white after closing the video in the main window of the browser
    • Bug 1582106 – PiP window conflicts with Youtube mini-player functionality
    • Bug 1582502 – Picture-In-Picture: when in fullscreen we can enable pip
    • Bug 1568216 – Rework/Improve PiP context menu options
  • In Progress
    • Bug 1585769 – Attempting to open some videos in the Picture-in-Picture player results in an all-white player window and SecurityError: The operation is insecure error
  • Investigating
    • Bug 1562218 – [Intermittent] PiP window displays only a white border instead of a video


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