Firefox for Web Developers

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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npub1ptjssujfd9duejv9gjx7mw4kxr4fw73vcusz7733ll72xcdpxtvqsg2wss

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[email protected]

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nprofile1qqsq4eggwfykjk7vexz5fr0dh2mrp65h0gkvwgp00gclll9rvxsn9kqpz3mhxue69uhhyetvv9ujuerpd46hxtnfduqs6amnwvaz7tmwdaejumr0ds384jj0

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relay.damus.io

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npub1ptjssujfd9duejv9gjx7mw4kxr4fw73vcusz7733ll72xcdpxtvqsg2wss

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Last Notes

2026-10-19 13:15:37 GMT

What should we ship in 2027? Rank your favourite features & create your wishlist: https://interop-rank.fxdx.dev/
https://files.mastodon.social/media_attachments/files/117/467/756/959/809/534/original/92efe2eafada7eab.mp4

2026-10-13 13:26:46 GMT

Firefox 158 landed today! For web developers, the highlights are:
🎉 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!
https://developer.mozilla.org/en-US/docs/Mozilla/Firefox/Releases/158

2026-10-08 13:30:17 GMT

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.
https://interop-rank.fxdx.dev/

2026-09-03 13:15:23 GMT

CSS attr() now works on all properties in Firefox 155. Here's how it works, and how to get the most out of it:
https://files.mastodon.social/media_attachments/files/117/207/289/604/113/445/original/845679b595169a1a.mp4

2026-08-25 13:03:43 GMT

CSS sibling-count() and sibling-index() are newly available across engines! Here's how they work:
https://files.mastodon.social/media_attachments/files/117/156/281/275/769/657/original/6c727e0329ed64e6.mp4

2026-08-24 11:49:04 GMT

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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: https://random-stuff.jakearchibald.com/apps/partial-img-decode/?demo=fox-progressive.jxl&density=2

2026-08-20 13:04:19 GMT

What should happen with text-box-trim and margin-trim when it comes to negative values? Do negatives 'trim'?
https://files.mastodon.social/media_attachments/files/117/127/972/180/216/495/original/627b1697c744c744.mp4

2026-08-19 13:15:16 GMT

CSS text-box is newly baseline, and it's solves a common text layout issue. Here's how it works:
https://files.mastodon.social/media_attachments/files/117/122/354/494/838/019/original/a46278cd41a08b1c.mp4

2026-08-18 13:15:05 GMT

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! https://developer.mozilla.org/en-US/docs/Mozilla/Firefox/Releases/154

2026-08-04 12:12:57 GMT

JS promise integration for WebAssembly landed in Firefox 153, making it easier to work with asynchronous calls from Wasm. Here's how it works:
https://files.mastodon.social/media_attachments/files/117/037/175/518/156/979/original/f7bf149ee659bff9.mp4

2026-07-21 16:19:04 GMT

The official Firefox account is back on fedi!
(I mean, this one is official too, but… you know what I mean)
#nevent1q…3ytr

2026-07-21 12:22:22 GMT

Firefox 153 just landed, and comes with web platform features like:
🎉 popover="hint"
🎉 Picture-in-picture
🎉 IDB getAllRecords()
🎉 JS Promise Integration for wasm
🎉 JS import-as-text
…And more! https://developer.mozilla.org/en-US/docs/Mozilla/Firefox/Releases/153

2026-07-16 08:35:21 GMT

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@nprofile…3q9y @nprofile…4fmn it's basically to make the user aware that it isn't something you'd expect from every website, and only something you should accept from a site you really trust https://hacks.mozilla.org/2026/05/web-serial-support-in-firefox/#:~:text=To%20help,access,-%2E

2026-07-16 08:13:23 GMT

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@nprofile…4fmn WebSerial tends to skew more towards hobby/tinkerer devices, whereas WebUSB can touch more general consumer devices, so as a browser that cares deeply about user safety, it made sense to do WebSerial and WebMIDI first.

2026-07-16 08:03:38 GMT

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@nprofile…4fmn one API at a time 😀

2026-07-14 09:00:49 GMT

Generally: Using Firefox Nightly (with analytics on), and reporting bugs to Bugzilla, is a _huge_ way to contribute to Firefox.
Firefox Nightly is more stable than other browser's Nightlies, and for a technical user it totally possible to use it as your main browser.
For your specific case, it seems like there's a bunch of UI issues relating to a particular form-factor & OS - I think it's ok to file a single issue to collate those. We can break them out if needed.

2026-07-09 13:15:22 GMT

Notification actions landed in Firefox 152, allowing you to add quick action buttons to your notifications. Here's how they work:
https://files.mastodon.social/media_attachments/files/116/890/200/511/099/201/original/b8e771b5a3a9141d.mp4

2026-06-17 14:37:19 GMT

CSS field-sizing is newly baseline, meaning you can make various form fields size to their contents, without needing JavaScript.
https://files.mastodon.social/media_attachments/files/116/765/951/184/616/379/original/5ff19e6ef7d549f7.mp4

2026-06-15 14:20:18 GMT

If your content is served over HTTP/3, make sure your DNS record advertises it, otherwise you're missing out on free performance.
Check your site here: https://savearoundtrip.com/

2026-06-02 13:45:23 GMT

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@nprofile…xa9x thanks for raising this. I'll do another video on it when this hits release (and probably another when it's baseline), and I'll include this point.

2026-06-02 13:23:20 GMT

Ever struggled to get heading tags right in includes/components? headingoffset could be the answer…
https://files.mastodon.social/media_attachments/files/116/680/726/249/279/715/original/12fe82eea056a0de.mp4

2026-05-28 15:19:16 GMT

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@nprofile…y6jc which sites do you use that use it, or what are your use-cases for it as a developer?

2026-05-28 15:01:21 GMT

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@nprofile…y6jc Web Serial is the second API we've applied this new permission flow to, the other being WebMIDI. We'll continue to look at other APIs on an individual basis.

2026-05-28 14:57:36 GMT

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@nprofile…y6jc what do you mean by 'ok' here?

2026-05-28 14:37:49 GMT

The Web Serial API landed in Firefox 151, allowing you to connect directly to microcontrollers, dev boards, 3D printers, power meters, and other serial-connected hardware from the web. Here's how it works:
https://files.mastodon.social/media_attachments/files/116/652/704/717/961/290/original/e87d6dbb51b31662.mp4

2026-05-21 18:58:02 GMT

Web Serial landed in Firefox 151! Here's how it works, and what you can do with it: https://hacks.mozilla.org/2026/05/web-serial-support-in-firefox/

2026-05-20 13:18:58 GMT

CSS style() queries landed in Firefox 151 making them newly available across engines. Here's how they work:
https://files.mastodon.social/media_attachments/files/116/607/098/808/055/668/original/147b41d0f16ea9f3.mp4

2026-05-19 13:00:25 GMT

Firefox 151 is out now, and brings with it some tasty new web platform features:
🎉 Container style() queries
🎉 Web Serial API
🎉 Document Picture-in-Picture API
🎉 keyboardLock on requestFullscreen
…and more!
https://developer.mozilla.org/en-US/docs/Mozilla/Firefox/Releases/151

2026-05-18 14:28:12 GMT

Chrome shipped an LLM Prompt API to the web platform. At Mozilla, we oppose this API. Here's why:
https://files.mastodon.social/media_attachments/files/116/596/046/915/658/563/original/d4a1d879483c971c.mp4

2026-04-30 09:04:38 GMT

Chrome looks set to ship an LLM Prompt API to the web platform. At Mozilla, we oppose this API.
We feel it has a large interoperability risk, and Google imposing T&Cs on a web API sets a dangerous precedent.
Full details: https://github.com/mozilla/standards-positions/issues/1213#issuecomment-4347988313

2026-04-27 13:15:34 GMT

CSS's light-dark() now accepts images, making it simpler to define alternate values for a dark color scheme. Here's how it works:
https://files.mastodon.social/media_attachments/files/116/476/851/633/664/514/original/1f14113b4b661b47.mp4

2026-04-23 13:08:32 GMT

sizes="auto" landed in Firefox 150, making responsive images simpler and more reliable. Here's when you can use it, and how…
https://files.mastodon.social/media_attachments/files/116/454/176/016/291/077/original/cf5d4285df90203f.mp4

2026-04-21 13:10:50 GMT

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@nprofile…tkx6 short story: it's easier for users to understand. Semver doesn't really make sense for a web engine. Whether each release should be a point release or 'major' release would be a lengthy debate and ultimately doesn't help users.

2026-04-21 11:06:25 GMT

Firefox 150 just landed & includes new web platform features like:
🎉 sizes="auto" on images
🎉 light-dark() image support
🎉 CSS revert-rule
🎉 ariaNotify()
🎉 Media pseudo-classes like :playing
None of these are baseline yet, so check MDN for support.
https://developer.mozilla.org/en-US/docs/Mozilla/Firefox/Releases/150

2026-04-01 08:11:29 GMT

Can you tell CSS from BS? I tried, and it's hard.
https://indieweb.social/@keithamus/116328410312008711
https://files.mastodon.social/media_attachments/files/116/328/431/622/325/897/original/2ae7b5b54118981e.mp4

2026-03-23 15:30:57 GMT

There are many browsers, but only three widely-used engines. We maintain one of those engines - Gecko. Here's why we feel that browser engine diversity is essential for the future of the web https://blog.mozilla.org/netpolicy/2026/03/23/competition-innovation-and-the-future-of-the-web/

2026-02-13 09:34:51 GMT

If you had to pick _one_, which web platform feature would you like in Firefox that isn't part of the Interop 2026 effort? https://hacks.mozilla.org/2026/02/launching-interop-2026/#new-features

2026-02-12 17:20:50 GMT

Here's a quick rundown of what we delivered as part of Interop 2025, and what's planned for Interop 2026!
More details on the features and focus areas: https://hacks.mozilla.org/2026/02/launching-interop-2026/
https://files.mastodon.social/media_attachments/files/116/058/805/582/758/267/original/be63a66a85008f17.mp4

2026-02-02 17:16:05 GMT

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@nprofile…xa9x ugh, the poster I used didn't give me the opportunity to add alt text. I've edited it to add your text - thank you.

2026-02-02 17:04:39 GMT

AI Controls (formally 'kill switch') are landing in today's Firefox Nightly, and will land with Firefox 148 later this month.
For the full details, see the Firefox blog https://blog.mozilla.org/en/firefox/ai-controls/
https://files.mastodon.social/media_attachments/files/116/002/119/428/537/379/original/5dcfa9e0a8ba85a4.mp4

2026-01-19 09:34:20 GMT

View Transition Types are newly baseline! These make it easier to build transitions that are specific to particular situations.
https://developer.mozilla.org/en-US/docs/Web/API/View_Transition_API/Using_types
Also, we have some new View Transition DevTools in Firefox 147…
https://files.mastodon.social/media_attachments/files/115/921/071/033/356/413/original/fadc2b5d093fc2ca.mp4

2026-01-14 10:31:22 GMT

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@nprofile…556c the communication around that commit was poor, but Firefox's commitment to privacy stands https://www.mozilla.org/en-US/privacy/firefox/.
The previous wording wasn't clear in terms of things like the Google search deal, for which Mozilla receives money, and Google does profit from advertising and user data.

2026-01-13 16:06:09 GMT

CSS anchor positioning is newly baseline! This opens the door for lots of new creative CSS.
It's a huge feature, but here are the basics.
https://files.mastodon.social/media_attachments/files/115/888/634/048/778/836/original/d42f44a8e1f1d07e.mp4

2025-12-18 12:36:01 GMT

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@nprofile…u25l I hope that the regular content here shows that folks are still working hard on web platform features. In some cases shipping sooner than browsers backed by the world's richest companies.

2025-12-18 12:11:21 GMT

Something that hasn't been made clear: Firefox will have an option to completely disable all AI features.
We've been calling it the AI kill switch internally. I'm sure it'll ship with a less murderous name, but that's how seriously and absolutely we're taking this.
…

2025-12-18 08:37:57 GMT

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@nprofile…9w26 to quote HTMX themselves (https://x.com/htmx_org/status/2001392286882808085)
> I'd say this functionality is orthogonal to htmx (and the two should play well together I hope!)

2025-12-16 16:26:21 GMT

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And check out MDN for the full documentation https://developer.mozilla.org/en-US/docs/Web/API/Invoker_Commands_API

2025-12-16 16:24:41 GMT

HTML invoker commands are newly baseline! Here's how they work…
https://files.mastodon.social/media_attachments/files/115/730/147/616/175/500/original/de4da486da9c8266.mp4

2025-12-12 15:31:05 GMT

❓ Do you have a need for range inputs with 3+ sliders on the web? Folks are scoping out this work, and want to know your use-cases ⬇️ https://github.com/openui/open-ui/issues/1337

2025-12-12 07:46:37 GMT

In Firefox 146 DevTools, long lists of unused CSS custom properties collapse, decluttering the UI, and improving performance.
https://files.mastodon.social/media_attachments/files/115/705/484/950/871/114/original/1ddbcbe905c5fb13.mp4

2025-12-09 15:57:54 GMT

CSS @scope has landed in Firefox 146, making it a new baseline feature. Here's how it works:
https://files.mastodon.social/media_attachments/files/115/690/427/909/270/430/original/4a91e961b8d2017e.mp4

2025-12-05 13:38:34 GMT

Oh hello! We've had a bit of a rename & rebrand (formally FirefoxDevTools), but the content will be roughly the same as it's been for the past few months.
We're looking forward to posting more on web platform & DevTools features.