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Firefox DevTools Newsletter — 114

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Developer Tools help developers write and debug websites on Firefox. This newsletter gives an overview of the work we’ve done as part of the Firefox 114 Nightly release cycle.

Firefox being an open source project, we are grateful to get contributions from people outside of Mozilla:

  • Vasilij Alexsandrovich made changes to our shared Tab component so selecting a tab in the overflow menu will make it visible (bug)
  • omid rad fixed the “copy as cURL” command to include the --compressed argument if the response was compressed (bug)
  • Ivan Simplify overly complicated InactivePropertyHelper#hasVerticalWritingMode (bug)

DevTools are written in HTML, CSS and JS so any web developer can contribute! Read how to setup the work environment and check the list of mentored issues



In the Accessibility panel, we used to display internal Gecko role, which were a bit cryptic.

Accessibility panel displaying the role tree. A lot of the roles are "landmark"
Accessibility Panel in Firefox 113 – Many roles have the Gecko internal, generic, “landmark” role

We’re now showing ARIA roles (main, navigation, …), which should be more helpful for web developers (bug).

Accessibility panel displaying the role tree. Instead of the "landmark" roles that were displayed before, we now have proper ARIA roles ("banner", "navigation", "search", …)
Accessibility Panel in Firefox 114 – ARIA roles are now being displayed, making it a lot more useful

Our MDN friends wrote a lovely article about landmark roles if you want to learn more about them.

Since we’re talking about accessibility, we changed the style of our links in all panels in order to pass WCAG Success Criterion 1.4.1 Use of Color (bug, bug). The underline is applied to links so they can be easily identified, specially for folks who cannot perceive color differences


Performance is a high concern for our team and we’re always looking for ways to improve the responsiveness of DevTools. We’re pleased to report that a refactoring of our node walker implementation made some operations in the inspector 10% faster ⚡️ (bug)

Graph of inspector performance test over time, shown for the April 6 to April 15 range
Around April 10, the numbers go from around 750ms to 650ms
Lower is better

Speaking of the Inspector, we now display media import conditions for @import CSS rules (bug)

Inspector rule view, displaying a rule that was imported via a `@import` with a `screen and (with > 10px)` condition.
The `@import screen and (with > 10px)` is displayed before the rule selector (in this case, `h1`)

In the Debugger Sources panel, ignored files now have a distinct style

The debugger Source tree, with ignored files having a crossed file icon and a yellow/brown color
console-test-animation.js and console-test-event-listeners.js are ignored, hence their different styling

We made a few small improvements to the pretty print feature. It doesn’t add line break for empty object and array literals anymore (bug), it adds a space character between of and [ (bug), and after => (bug), and it better handles the spread operator on array literal (bug).


Miscellaneous bug fixes:

  • Don’t always select original source on pause (bug)
  • Source Tree “Ignore” context menu labels were not updated after ignoring a file (bug)
  • Prevent Stylesheet visibility toggle to be hidden because of long stylesheet names (bug)
  • Storage inspector sidebar could be fully collapsed (bug)

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