Firefox for Web Developers
@webdevs.firefox.com
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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Firefox 159 release notes for developers (Stable) - Mozilla | MDN
This article provides information about the changes in Firefox 159 that affect developers. Firefox 159 was released on October 27, 2026.
developer.mozilla.org
Firefox 159 has landed! This is a pretty big one for web dev stuff:
🎉 CSS scroll-driven animations, both scroll() and view().
🎉 Scoped custom element registries.
🎉 Streaming sanitization of HTML.
And more! developer.mozilla.org/en-US/docs/M...
🎉 CSS scroll-driven animations, both scroll() and view().
🎉 Scoped custom element registries.
🎉 Streaming sanitization of HTML.
And more! developer.mozilla.org/en-US/docs/M...
Scroll-driven animations are newly available in all major engines! Here's how they work:
October 28, 2026 at 2:53 PM
Scroll-driven animations are newly available in all major engines! Here's how they work:
Firefox 159 has landed! This is a pretty big one for web dev stuff:
🎉 CSS scroll-driven animations, both scroll() and view().
🎉 Scoped custom element registries.
🎉 Streaming sanitization of HTML.
And more! developer.mozilla.org/en-US/docs/M...
🎉 CSS scroll-driven animations, both scroll() and view().
🎉 Scoped custom element registries.
🎉 Streaming sanitization of HTML.
And more! developer.mozilla.org/en-US/docs/M...
Firefox 159 release notes for developers (Stable) - Mozilla | MDN
This article provides information about the changes in Firefox 159 that affect developers. Firefox 159 was released on October 27, 2026.
developer.mozilla.org
October 27, 2026 at 2:15 PM
Firefox 159 has landed! This is a pretty big one for web dev stuff:
🎉 CSS scroll-driven animations, both scroll() and view().
🎉 Scoped custom element registries.
🎉 Streaming sanitization of HTML.
And more! developer.mozilla.org/en-US/docs/M...
🎉 CSS scroll-driven animations, both scroll() and view().
🎉 Scoped custom element registries.
🎉 Streaming sanitization of HTML.
And more! developer.mozilla.org/en-US/docs/M...
JPEG XL is newly available in all major engines, but how does it stack up against other formats?
October 26, 2026 at 2:16 PM
JPEG XL is newly available in all major engines, but how does it stack up against other formats?
What should we ship in 2027? Rank your favourite features & create your wishlist: interop-rank.fxdx.dev
October 19, 2026 at 1:15 PM
What should we ship in 2027? Rank your favourite features & create your wishlist: interop-rank.fxdx.dev
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/docs/M...
🎉 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/docs/M...
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.
developer.mozilla.org
October 13, 2026 at 1:26 PM
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/docs/M...
🎉 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/docs/M...
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
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
interop-rank.fxdx.dev
October 12, 2026 at 9:22 AM
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
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
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
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
Interop Feature Ranking
Rank the web platform features you care most about
interop-rank.fxdx.dev
October 8, 2026 at 1:30 PM
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
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
Firefox 157 has landed, and includes a couple of useful CSS features:
🎉 at-rule() in @supports - lets you limit rules to browsers that support a given at-rule.
🎉 overscroll-behavior: chain - lets scrolling pass up to parent elements, but prevents UA effects like 'bounce' and overscroll.
…And more!
🎉 at-rule() in @supports - lets you limit rules to browsers that support a given at-rule.
🎉 overscroll-behavior: chain - lets scrolling pass up to parent elements, but prevents UA effects like 'bounce' and overscroll.
…And more!
Firefox 157 release notes for developers (Stable) - Mozilla | MDN
This article provides information about the changes in Firefox 157 that affect developers. Firefox 157 was released on September 29, 2026.
developer.mozilla.org
September 29, 2026 at 1:15 PM
Firefox 157 has landed, and includes a couple of useful CSS features:
🎉 at-rule() in @supports - lets you limit rules to browsers that support a given at-rule.
🎉 overscroll-behavior: chain - lets scrolling pass up to parent elements, but prevents UA effects like 'bounce' and overscroll.
…And more!
🎉 at-rule() in @supports - lets you limit rules to browsers that support a given at-rule.
🎉 overscroll-behavior: chain - lets scrolling pass up to parent elements, but prevents UA effects like 'bounce' and overscroll.
…And more!
Reposted by Firefox for Web Developers
When and how CSS custom property values are calculated might not be what you expect, and it has a big impact on your styles…
September 10, 2026 at 1:23 PM
When and how CSS custom property values are calculated might not be what you expect, and it has a big impact on your styles…
When and how CSS custom property values are calculated might not be what you expect, and it has a big impact on your styles…
September 10, 2026 at 1:23 PM
When and how CSS custom property values are calculated might not be what you expect, and it has a big impact on your styles…
Reposted by Firefox for Web Developers
Great news 🤩
For anyone interested in how to use progress in fluid typography @matthewmorete.com made an excellent post about it here 👇
blog.master.dev/fluid-typogr...
For anyone interested in how to use progress in fluid typography @matthewmorete.com made an excellent post about it here 👇
blog.master.dev/fluid-typogr...
Fluid Typography with progress()
With the `progress()` function in CSS we've got a new way to calculate the size for type based on the viewport without problems of the past.
blog.master.dev
September 8, 2026 at 9:21 PM
Great news 🤩
For anyone interested in how to use progress in fluid typography @matthewmorete.com made an excellent post about it here 👇
blog.master.dev/fluid-typogr...
For anyone interested in how to use progress in fluid typography @matthewmorete.com made an excellent post about it here 👇
blog.master.dev/fluid-typogr...
The CSS progress() function is now in all major engines! Here's how it works:
September 8, 2026 at 1:15 PM
The CSS progress() function is now in all major engines! Here's how it works:
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...
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.
github.com
September 3, 2026 at 4:34 PM
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...
CSS attr() now works on all properties in Firefox 155. Here's how it works, and how to get the most out of it:
September 3, 2026 at 1:16 PM
CSS attr() now works on all properties in Firefox 155. Here's how it works, and how to get the most out of it:
Reposted by Firefox for Web Developers
I love this tool @webdevs.firefox.com devtools - so useful in the browser as a drag and design tool.
Also, new speaker drop… "drop", announcement I think…
Also, new speaker drop… "drop", announcement I think…
September 2, 2026 at 11:56 AM
I love this tool @webdevs.firefox.com devtools - so useful in the browser as a drag and design tool.
Also, new speaker drop… "drop", announcement I think…
Also, new speaker drop… "drop", announcement I think…
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/docs/M...
🎉 Fully typed CSS attr()
🎉 CSS progress()
🎉 Promise.allKeyed() and allSettledKeyed()
🎉 Lots of new WebTransport stuff
…And more!
developer.mozilla.org/en-US/docs/M...
Firefox 155 release notes for developers (Stable) - Mozilla | MDN
This article provides information about the changes in Firefox 155 that affect developers. Firefox 155 was released on September 1, 2026.
developer.mozilla.org
September 1, 2026 at 1:15 PM
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/docs/M...
🎉 Fully typed CSS attr()
🎉 CSS progress()
🎉 Promise.allKeyed() and allSettledKeyed()
🎉 Lots of new WebTransport stuff
…And more!
developer.mozilla.org/en-US/docs/M...
CSS sibling-count() and sibling-index() are newly available across engines! Here's how they work:
August 25, 2026 at 1:03 PM
CSS sibling-count() and sibling-index() are newly available across engines! Here's how they work:
JPEG XL is slated to ship in Firefox 157 next month! Here's how we're shipping it safely… hacks.mozilla.org/2026/08/inte...
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…
hacks.mozilla.org
August 24, 2026 at 3:38 PM
JPEG XL is slated to ship in Firefox 157 next month! Here's how we're shipping it safely… hacks.mozilla.org/2026/08/inte...
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.or...
This includes key JPEG XL features like progressive rendering.
groups.google.com/a/mozilla.or...
Intent to ship: JPEG XL
As of Firefox 157 I intend to turn JPEG XL decoding on by default on all platforms. It has been developed behind image.jxl.enabled, which today is on by default on Nightly only, and has had a Firefox…
groups.google.com
August 24, 2026 at 11:49 AM
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.or...
This includes key JPEG XL features like progressive rendering.
groups.google.com/a/mozilla.or...
What should happen with text-box-trim and margin-trim when it comes to negative values? Do negatives 'trim'?
August 20, 2026 at 1:03 PM
What should happen with text-box-trim and margin-trim when it comes to negative values? Do negatives 'trim'?
CSS text-box is newly baseline, and it's solves a common text layout issue. Here's how it works:
August 19, 2026 at 1:19 PM
CSS text-box is newly baseline, and it's solves a common text layout issue. Here's how it works:
Firefox 154 landed today, and brings with it some great web platform features:
🎉 CSS text-box
🎉 CSS sibling-index() and sibling-count()
🎉 JS Iterator methods like chunks, window, includes, & join
🎉 HTTP No-Vary-Search
…And more! developer.mozilla.org/en-US/docs/M...
🎉 CSS text-box
🎉 CSS sibling-index() and sibling-count()
🎉 JS Iterator methods like chunks, window, includes, & join
🎉 HTTP No-Vary-Search
…And more! developer.mozilla.org/en-US/docs/M...
Firefox 154 release notes for developers (Stable) - Mozilla | MDN
This article provides information about the changes in Firefox 154 that affect developers. Firefox 154 was released on August 18, 2026.
developer.mozilla.org
August 18, 2026 at 1:15 PM
Firefox 154 landed today, and brings with it some great web platform features:
🎉 CSS text-box
🎉 CSS sibling-index() and sibling-count()
🎉 JS Iterator methods like chunks, window, includes, & join
🎉 HTTP No-Vary-Search
…And more! developer.mozilla.org/en-US/docs/M...
🎉 CSS text-box
🎉 CSS sibling-index() and sibling-count()
🎉 JS Iterator methods like chunks, window, includes, & join
🎉 HTTP No-Vary-Search
…And more! developer.mozilla.org/en-US/docs/M...
We have an open position for a student worker on the Firefox Networking team in Germany. We work on the full stack, from high level HTTP all the way down to TCP/UDP. Some C++, some Rust. If that interests you, here are the details: www.mozilla.org/en-US/career...
Mozilla Careers — Necko Student Worker — Open Positions
Mozilla is hiring a Necko Student Worker in Remote Canada, Firefox, New Products, Firefox, Core Services, Infrastructure, Mozilla.org, New Products, Marketing,…
www.mozilla.org
August 11, 2026 at 1:44 PM
We have an open position for a student worker on the Firefox Networking team in Germany. We work on the full stack, from high level HTTP all the way down to TCP/UDP. Some C++, some Rust. If that interests you, here are the details: www.mozilla.org/en-US/career...
JS promise integration for WebAssembly landed in Firefox 153, making it easier to work with asynchronous calls from Wasm. Here's how it works:
August 4, 2026 at 12:14 PM
JS promise integration for WebAssembly landed in Firefox 153, making it easier to work with asynchronous calls from Wasm. Here's how it works:
JS text imports landed in Firefox 153, making it the first browser to support this feature. Here's how it works:
July 30, 2026 at 12:39 PM
JS text imports landed in Firefox 153, making it the first browser to support this feature. Here's how it works: