A tab preview showing the page contents of another background tab
Categories: News

A Preview of Tab Previews – These Weeks in Firefox: Issue 153


  • Tab Previews! Congratulations to DJ for getting these landed. Currently disabled by default, but you can test them by setting `browser.tabs.cardPreview.enabled` to true

A tab preview showing the page contents of another background tab

A comparison showing increased contrast and lower brightness for images displayed in dark theme Reader Mode

Increased contrast and reduced brightness make images easier on the eyes (right: old changes, left: new changes)

Friends of the Firefox team

Resolved bugs (excluding employees)

Script to find new contributors from bug list

Volunteers that fixed more than one bug

  • Gregory Pappas [:gregp]

New contributors (🌟 = first patch)

Project Updates

Add-ons / Web Extensions

Addon Manager & about:addons
  • Thanks to Anna Yeddi, a missing label to the remove shortcut icon from the extensions shortcuts management view part of the about:addons page has been identified and added. Another accessibility issue caught by the a11y jobs 🥳 – Bug 1873304
WebExtensions Framework
  • As part of follow ups to the work on the new taskcluster jobs to run webextensions tp6 and tp6m perftests jobs (landed as tier-3 jobs as part of Bug 1859549 in December):
    • A new linter named condprof-addons has been landed, this new linter makes sure that xpi files referenced in condprof customization files and the firefox-addons.tar archive (fetched through the related CI fetch task) are not going out of sync with each other – Bug 1868144
      • The condprof-addons linter is documented here
      • Thanks to ahal and sparky for their help and support on introducing this new linter
    • A new doc section has been added to the Raptor Browsertime doc page, to briefly provide a description of the webextensions tp6/tp6m perftests jobs and examples for how to run these tests locally and in try pushes – Bug 1874487
      • The new section is already available here

Developer Tools

  • Alex added a notice at the bottom of the Debugger editor when the source map file is invalid or unavailable (bug)

Notification about a Source Map Error due to an unexpected non-whitespace character

  • Hubert delayed getting information about sources functions until we need to display them, which made opening files faster (bug)
  • Hubert fixed an issue where the Debugger would crash (bug)
  • Alex added options to the console :trace command limit depth and number of top level frames being traced (bug)
    • (still behind devtools.debugger.features.javascript-tracing)
    • :trace –max-depth N –max-records M
  • Alex improved performance of the console when it’s receiving a very large number of messages (bug, bug)
  • Nicolas made Ctrl+Enter (Cmd+Enter on MacOS) on Rules view input advance the focus to the next editable property, i.e. like the Tab key (bug)
  • Nicolas added a hint about the new Enter key behavior in Rules view input, linking to an explanatory blog post (bug)

Notification explaining that Enter key no longer changes focus in Rules view

WebDrive BiDi
  • Julian added support the the network.fetchError event, which is emitted when a request ends in an error state (bug)
  • Julian implemented the network.failRequets command, which forces an intercepted request to fail, and will fire a network.fetchError event (bug)
  • Sasha made script.evaluate, script.callFunction and script.disown ignore the realm argument when a context argument is passed (bug)
  • Henrik fixed an issue with the browsingContext.create command, aligning with Chrome for a consistent cross-browser experience (bug)

ESMification status

  • Some changes landed after today’s numbers were generated (see new tab page section below) – that brings us to the 90% mark on browser/
  • ESMified status:
    • browser: 89%
    • toolkit: 99%
    • Total:  96.48% (no change)
  • #esmification on Matrix

Lint, Docs and Workflow

Migration Improvements

  • The next wave of spotlight messages to encourage users without accounts to create one to aid in device migration should be going out in a week or so.
  • The infrastructure that allows for doing backups of active SQLite databases has landed. We’re hoping this can be part of the foundations for a backup-to-local-file utility.

New Tab Page


  • emilio landed some patches that fix a regression with kde/wayland window rules for the PiP window not working as intended (bug)


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5 comments on “A Preview of Tab Previews – These Weeks in Firefox: Issue 153”

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  1. Midori wrote on

    Wow!! it’s such a perfect feature for displaying tabs. This should have been landed several years ago.

    Thank you Mozillian


  2. jonzn4SUSE wrote on

    I’m wondering if this will impact performance. You know there are users out there complaining about FISSION.


    1. jonzn4SUSE wrote on

      Does it only work on Wikipedia?


  3. jonzn4SUSE wrote on

    I see. The tab has to refresh before the preview shows.


  4. jonzn4SUSE wrote on

    This feature has synced from Nightly to all other versions of Firefox and works well.


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