Categories: News

These Weeks in Firefox: Issue 63


Mockup of the new warning UI on the about:addons page

  • The new DOM Mutation Breakpoint feature allows the user to pause JS execution when the DOM structure changes. It’s now available behind a flag and ready for testing in Nightly! You need to flip the two following prefs to enable it:
    • devtools.debugger.features.dom-mutation-breakpoints devtools.markup.mutationBreakpoints.enabled
Mockup of the new context menu entry to create DOM breakpoint

Use the Inspector panel context menu to create new DOM Mutation Breakpoints

Mockup of the DOM breakpoint list in a side pane of the debugger

Use the debugger side panel to see existing DOM Mutation Breakpoints.

  • Inline Previews in the Debugger – showing actual variable values inline. This feature is also available behind a flag and ready for testing. You need to flip the following pref to enable it:
    • Devtools.debugger.features.inline-preview
Inline preview of variable values in the debugger showcased on example code.

Note the inline boxes showing actual variable values


Friends of the Firefox team

Resolved bugs (excluding employees)

Fixed more than one bug

  • Arun Kumar Mohan
  • Dennis van der Schagt [:dennisschagt]
  • Dhyey Thakore [:dhyey35]
  • Florens Verschelde :fvsch
  • Heng Yeow (:tanhengyeow)
  • Itiel
  • Krishnal Ciccolella
  • Megha [ :meghaaa ]
  • Priyank Singh

New contributors (🌟 = first patch)

Project Updates

Add-ons / Web Extensions

Mockup of the extension storage view in the storage tab of the devtools

Developer Tools

  • Disable debugger; statement – It is now possible to disable a debugger statement via a false-conditional breakpoint created at the same location (bug).
  • WebSocket Inspection (GSoC project) – This feature is enabled on Nightly by default (devtools.netmonitor.features.webSockets)
    • Supported protocols Socket.IO, SockJS, plain JSON (and MQTT soon)
    • WS frames Filtering supported (by type & by free text)
    • A test page

Mockup of the new view in the devtools network tab showing websocket messages

  • Heads Up: Search across all files/cookies/headers in the Network panel coming soon! (Outreachy)
Perf Tools
  • JavaScript Allocations – tracking for JS allocations added. It’s still experimental but you can enable it by checking “JS Allocations” in recording panel feature flags

JavaScript allocations shown in a tree view in the Devtools Performance tab.


Accessibility Panel
  • A new option to auto-scroll to the selected node has been added to the panel tree

Screenshot showing a new "Scroll into view" option in the settings context menu of the Acccessibility Panel of the Devtools.



  • ESLint has been updated to 6.1.0 (from 5.16.0). This helped us with a few things:
    • Running –fix over the entire tree should now work for pretty much everything that’s auto-fixable. Previously it would stop working at the `js/` directories, and then you’d have to run it manually on the remaining sub-directories (e.g. services, toolkit etc etc).
    • If you have an /* global foo */ statement for ESLint and foo is unused, it will now throw an error.
    • There’s also now a new rule enabled on most of the tree: no-async-promise-executor. This aims to avoid issues with having asynchronous functions within new Promise()
  • ESLint will also be upgraded to 6.2.2 within the next couple of days. The main addition here is support for BigInt and dynamic imports.

New Tab Page

  • In Firefox 69 we’re launching “Discovery Stream” which is a newtab experience with more Pocket content. We’re doing this with a rollout on Sept 10th.

Password Manager




Search and Navigation

User Journey

Uplifted to 69 beta: Moments page, New Monitor snippet, Extended Triplets

No comments yet

Post a comment

Leave a Reply

Your email address will not be published. Required fields are marked *