These Weeks in Firefox: Issue 76


  • Call for testing: turn on the devtools.netmonitor.features.sse pref, which provides support for Server Side Events (SSE) ready in 80 and a visualization for text/event-stream content types (bug).
    • Use this test page #1
    • Use this test page #2 (with support for Mercure protocol)The network panel shows a server side event with five different data values. This includes "Hello world" with a few emojis, "Welcome to SSE Demo" with a few emojis, "This one will set an id 1", and two JSON objects are displayed under the response section

The more popup next to now displays "Import from a File..." in the dropdownImport login information, it’s easy!

The login prompt displays three saved usernames:, John, and DoeCheck out all of your saved usernames!

  • Check out a blog post on how we improved Firefox startup time with the about:home startup cache. Enable this by going to about:preferences#experimental and continue filing bugs.
  • Console – A new :block command for blocking requests is now available in the Console panel (Thanks to thelehhman).
    • :block app.css

The network panel now has a "Do not enter" icon. When enabled, this creates a "blocking" section that shows "app.css" checked. In the box to the right, app.css is displayed in red with a note "Blocked by Devtools." The filtered output also displays ":block app.css"

Friends of the Firefox team

Resolved bugs (excluding employees)

Fixed more than one bug

  • Andrew Park
  • Itiel
  • kenrick95
  • Sonia

New contributors (🌟 = first patch)

Project Updates

Add-ons / Web Extensions

Addon Manager & about:addons
  • Share fixed a couple of issues that were preventing addons from being installed or updated when the builtin cert was not being used (which is the case for some organizations that use their own certificates, or because of some antivirus that install its own certificate to inspect HTTPS connections) – Bug 1647360 and Bug 1648815
  • Will Durand made sure that the sourceURL in the addon abuse reports submitted by users will be set to the expected source url even when the website did change it using the history API – Bug 1648036
  • Andrew Park contributed a fix that prevents the addon download doorhanger to show “NaN bytes/sec” when the download starts – Bug 1544570
WebExtensions Framework
  • Agi fixed a perf issue related to main thread I/O on startup when the rkv-based ExtensionPermissions backend is in use (only Nightly at the moment) – Bug 1651628 (main thread I/O originally introduced in Bug 1637680)
  • Landed an initial part of the changes needed to support Extension’s service workers and the manifest v3 background service workers (locked behind prefs “extensions.backgroundServiceWorker.enabled” and “extensions.service_worker_register.allowed”, currently both false by default on all channels) – Bug 1609920 (as a side note: even when enabled using the supported prefs no WebExtensions API are yet available in the Extension’s service workers)
WebExtension APIs
  • Rob fixed the validation of the chrome_settings_override’s search_url/suggest_url/search_form, which was allowing more than just localhost urls in those manifest properties – Bug 1651665 (landed in 80 and pending an uplift request to 79, where the originally regression landed, Bug 1612013)
  • Harsh Arora contributed a small fix to ensure that the API is going to log in the BrowserConsole unexpected errors raised internally when a download fails – Bug 1645337 (originally regressed by Bug 1576333)


  • We’ve identified a reliability issue with Send Tab. The fix is in review now, and will be likely deployed with the 7/28 release.

Developer Tools

  • Layout & Mobile Tools – XPath search now supports more expressions—previously, only expressions starting with a “/” were recognized.
    • Check this bug for more details (thanks to Sebo!)
  • Infrastructure improvements
    • Getting rid of message manager & framescript (thanks to Neil Deakin, bug, bug, bug, bug)
    • Codebase cleanup – removing old RDM UI (frame script, browser element, viewport, etc.)


  • Making progress with a unified Resource layer. Good progress on DevTools client side and starting also with the backend (server side).
  • Individual DevTools panels/tools  “watch” for specific resource types (console message, network request, debugger source, etc.) and get them from all debugged scopes automatically (content & main processes, workers, etc.)


Password Manager



  • Planning has begun to do some experiments regarding improved discoverability of the Picture-in-Picture toggle

User Journey

  • Launched about:welcome experiment in 78 with 2 screens (welcome and import)
    • Also testing new Amplitude integration and comparing with Redash
  • Adding additional experimental welcome screens for privacy and themes
  • Preparing some new default 80 welcome experience based on multistage findings
  • Turning on password import autocomplete suggestions by default in 80 with additional robustness over 77 experiment functionality (accessibility, localization)


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