Firefox DevTools

🚀 A bunch of #WebDriver features and fixes landed in Firefox 146. WebDriver is the W3C standard for interoperable browser automation, for things like testing tools, and MCPs. Keep up to date with all the progress here: fxdx.dev/firefox-webdri…

In Firefox 146 DevTools, long lists of unused CSS custom properties collapse, decluttering the UI, and improving performance

A bunch of web platform features and bug fixes landed in Firefox 146. There'll be more videos about the highlights soon, but in the meantime, here's a summary: developer.mozilla.org/en-US/docs/Moz…

CSS @​scope has landed in Firefox 146, making it a new baseline feature. Here's how it works:

We have Custom Elements, but do we also need Custom Attributes? This was discussed at TPAC. Is it something you'd like on the platform?

full update at fxdx.dev/firefox-webdri…

🚀 Firefox 145 introduces WebDriver BiDi enhancements like a new `emulation.setUserAgentOverride` command for spoofing user agents, a `browsingContext.downloadEnd` event to track completed downloads, plus various fixes. #Firefox #WebDriver

Last week I posted about a secret config in Firefox that made view transitions easier to debug. @SailorPsy said we should make it less secret. So we did.

New in Firefox nightly (146.0a1 2025-10-19): large lists of unused CSS custom properties are collapsed by default. This not only reduces clutter, it also massively speeds up the rendering of the inspector panel in some cases.

We're currently working on devtools for view transitions in Firefox, but in the meantime, here's a little-known option that helps…

🦊 Firefox 144 adds the screen orientation and timezone override commands + the downloadWillBegin event to WebDriver BiDi! fxdx.dev/firefox-webdri…

There are… a lot of proposals, but you don't need to rank them all. Skim through the list, and find the few you really care about. This is an experiment, so we're also interested in feedback on the app itself, and things we can improve for next year.

As an experiment, we (the Firefox team) wanted to try a new way to get feedback on which Interop proposals matter most. So, here's a web app where you can rank the proposals you care about, giving us data we can use when reviewing which ones to champion. interop-rank.jakearchibald.com

🦊 Firefox 143 was just released! Some WebDriver BiDi highlights: new commands to record and retrieve network responses, backfill events for `browsingContext.contextCreated` and, as usual, some bug fixes 🐛. More details at fxdx.dev/firefox-webdri… !

@amanushenkov Even just navigate from rule to rule with the arrow keys would be nice so you don't have to tab through everything

Would be kinda cool if you could navigate the rules tab in Vim-like manner ;)

If you have any bug reports or improvement suggestions, you can file a ticket under firefox devtools category at bugzilla.mozilla.org, or leave a comment here/dm me

Firefox 142 brings a few WebDriver BiDi and Classic updates: a new command to set the locale override, some changes around handling the cookies 🍪 and setting the proxy, and more at fxdx.dev/firefox-webdri… 🚀

@GoceMitevski @FirefoxNightly Can you file a bug please? bugzilla.mozilla.org/enter_bug.cgi?… Thanks!

Hey @FirefoxNightly, System theme — auto seems broken in the latest builds. It always remains in light mode and it never switches to dark. Testing on 141.0a1 (2025-06-09) at the moment, but this was broken with 140 afaik.

🦊 Freshly released Firefox 141 comes with a few WebDriver updates. Setup a proxy for a container with browser.createUserContext, monitor history API usage with browsingContext.historyUpdated. And also a few changes around Cookies. Read more at fxdx.dev/firefox-webdri… 🚀

A little while ago I added a little quality of life feature to @FirefoxDevTools . Now the network filter query persists between devtools instances! (you used to have to type it out every time) ticket: bugzilla.mozilla.org/show_bug.cgi?i… before & after:

🦊 In Firefox 140, WebDriver BiDi allows to override certificates security settings per container and supports a new "navigationCommitted" event. This release also brings a few fixes for action simulation. More details at fxdx.dev/firefox-webdri… 🚀