@FirefoxWebDevs

Official Firefox account for people who build on the web. Learn about the things we're working on to grow and improve the web platform.

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hacks.mozilla.org
Joined June 2009
  • Tweets8.1K
  • Following5.5K
  • Followers90.2K
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Firefox 158 landed today! For web devs: 🎉 JPEG XL support, including full progressive rendering. 🎉 'navigate' on notifications, so they can go to a URL without firing events. 🎉 WebGPU's float32-blendable 🎉 WebGL's EXT_polygon_offset_clamp And more! developer.mozilla.org/en-US/…

Firefox 158 release notes for developers (Stable) - Mozilla | MDN

This article provides information about the changes in Firefox 158 that affect developers. Firefox 158 was released on October 13, 2026.

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What should we ship in 2027? Rank your favourite features & create your wishlist: interop-rank.fxdx.dev/
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We've loved seeing folks post their rankings, so we've added a share button! You can either share your list via the site directly, or copy your list as markdown/html for your own blog. interop-rank.fxdx.dev/

2027 Web Platform Feature Ranking

Rank the Interop 2027 features you care most about

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What do you want us to work on in 2027? Here's a web app where you can rank the Interop proposals you care about, giving us data we can use to prioritise feature development. interop-rank.fxdx.dev/

2027 Web Platform Feature Ranking

Rank the Interop 2027 features you care most about

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We ran this last year to decide what to champion for Interop 2026, but the data was so good, we also used it to prioritise features beyond the Interop project. We've also added some features to make it quicker to rank items.
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Firefox 157 has landed, and includes a couple of useful CSS features: 🎉 at-rule() in @supports - limit rules to browsers that support a given at-rule. 🎉 overscroll-behavior: chain - allow chained scrolling without overscroll effects. …And more! developer.mozilla.org/en-US/…

Firefox 157 release notes for developers - Mozilla | MDN

This article provides information about the changes in Firefox 157 that affect developers. Firefox 157 was released on September 29, 2026.

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Firefox for Web Developers retweeted
Firefox for Web Developers
@FirefoxWebDevsSep 10
When and how CSS custom property values are calculated might not be what you expect, and it has a big impact on your styles…
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When and how CSS custom property values are calculated might not be what you expect, and it has a big impact on your styles…
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The CSS progress() function is now in all major engines! Here's how it works:
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Full docs on MDN: developer.mozilla.org/en-US/…

progress() CSS function - CSS | MDN

The progress() CSS function returns a value representing the position of one value (the progress value) relative to two other values (the progress start and end values).

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Interop 2027 is open for proposals! Is there a well-tested feature that you'd like to see cross-browser focus on next year? Submit it here: github.com/web-platform-test…

interop/proposal_guide.md at main · web-platform-tests/interop

web-platform-tests Interop project. Contribute to web-platform-tests/interop development by creating an account on GitHub.

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CSS attr() now works on all properties in Firefox 155. Here's how it works, and how to get the most out of it: instagram.com/reel/Dc05U1ilb…

Firefox for Web Developers (@firefoxwebdevs) • Instagram reel

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Major versions of Firefox now land every two weeks, so Firefox 155 dropped today with web platform features including: 🎉 Fully typed CSS attr() 🎉 CSS progress() 🎉 Promise.allKeyed() and allSettledKeyed() 🎉 Lots of new WebTransport stuff …And more! developer.mozilla.org/en-US/…

Firefox 155 release notes for developers - Mozilla | MDN

This article provides information about the changes in Firefox 155 that affect developers. Firefox 155 was released on September 1, 2026.

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Firefox for Web Developers retweeted
Jake Archibald@jaffathecakeAug 26
📝 When and how CSS custom properties are calculated might not be what you expect, and it has a big impact on your styles. Here's how it works: jakearchibald.com/2026/css-c…

Controlling when CSS custom property values are computed

The default might not be what you expect, and it has a big impact on your styles.

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CSS sibling-count() and sibling-index() are newly available across engines! Here's how they work:
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And the full docs on MDN: developer.mozilla.org/en-US/…

sibling-index() CSS function - CSS | MDN

The sibling-index() CSS function returns an integer representing the position of the current element in the DOM tree relative to all its sibling elements. The returned value is the index number of...

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JPEG XL is slated to ship in Firefox 157 next month! Here's how we're shipping it safely… hacks.mozilla.org/2026/08/in…

Intent to Ship: JPEG XL – Mozilla Hacks - the Web developer blog

A JPEG XL decoder is heading for Firefox 157! Here's how we're shipping it safely…

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Intent to ship: JPEG XL! This will be on-by-default in Firefox 157, which should become the main release version at the end of September. This includes key JPEG XL features like progressive rendering. groups.google.com/a/mozilla.…
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In a JPEG XL compatible browser (like Firefox Nightly), test how it renders progressively by moving the slider in this demo: random-stuff.jakearchibald.c…
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Chrome also has an Intent to Ship, so support should land in both browsers within a week of each other groups.google.com/a/chromium…
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