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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Last Notes

2026-06-16 14:15:05 GMT

Firefox 152 landed today, and includes web platform features like:
🎉 CSS field-sizing
🎉 Notification actions
🎉 unadjustedMovement pointer locks
🎉 getAnimations() pseudoElement option
…and more!
https://developer.mozilla.org/en-US/docs/Mozilla/Firefox/Releases/152

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 13:23:20 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

2026-06-01 14:08:01 GMT

We're experimenting with a way to visualize session history in Firefox DevTools, and we'd love your feedback!
Here's the background, and how to try it: https://blog.farre.se/posts/2026/06/01/session-history-diagrams/
https://files.mastodon.social/media_attachments/files/116/675/240/212/737/075/original/5cba1b0f5e5a1898.mp4

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

2026-05-20 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

2026-05-18 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

2026-03-26 14:38:35 GMT

hasUAVisualTransition landed in Firefox 149, making it available across all major engines. As well as having a very catchy name, it lets you avoid doubling up on page transitions. Here's how it works:
https://files.mastodon.social/media_attachments/files/116/295/980/096/103/884/original/411a24edc30e5286.mp4

2026-03-02 15:06:52 GMT

CSS shape() landed in Firefox 148. It's similar to path(), but allows the full expressiveness of CSS…
https://files.mastodon.social/media_attachments/files/116/160/200/898/847/330/original/75ea6466e5193fc7.mp4

2026-02-25 12:07:54 GMT

You can throw away innerHTML and replace it with the new setHTML(), which has a built-in sanitizer. Here's how it works:
https://files.mastodon.social/media_attachments/files/116/131/184/985/046/869/original/6c80e04b5cc9f08b.mp4

2026-02-16 14:45:37 GMT

HTML might be getting a new type of tag, which… hasn't happened this millennium. Here's the new syntax, and how it works.
And here's the explainer on HTML patching https://github.com/WICG/declarative-partial-updates/blob/main/patching-explainer.md
https://files.mastodon.social/media_attachments/files/116/080/843/869/386/478/original/32d1a22b837fa54a.mp4

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

2026-02-03 12:34:00 GMT

- reply

here's the help page, so you can judge for yourself https://support.mozilla.org/en-US/kb/firefox-ai-controls. We mostly refrain from using "opt-in" because people have different definitions of opt-in, e.g. some have said it's only opt-in if it's in a separate binary.
I asked for UI that shows downloaded models, but there wasn't time for that in 148. I'll keep asking for it 😀

2026-02-03 12:19:36 GMT

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I don't think it's particularly unusual to offer features at the point they might be useful. This follows the pattern of e.g. asking for microphone permission. You're asked at a time that it might be useful to you, you don't have to say yes, and there are ways to avoid ever being asked.

2026-02-03 12:07:23 GMT

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fwiw, the individual features are, to some extent, opt in. As in, AI models are not downloaded and used until you engage with the feature, e.g. via the "Suggest more of my tabs" button.
https://files.mastodon.social/media_attachments/files/116/006/610/433/200/223/original/bd12f5f4102a07ca.png

2026-02-02 22:58:16 GMT

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translation is valuable for reading parts of the web that aren't in a language you can understand. Tab group naming means you can select a bunch of tabs and the model tries to come up with a decent name. Generated alt text helps improve the accessibility of PDF documents.

2026-02-02 22:44:34 GMT

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Sad to see you go. Fwiw, LibreWolf has translation very similar to Firefox's, which most users consider to be AI.

2026-02-02 19:21:51 GMT

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I'm not sure what we can do to convince you other than hold the promise over time.

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

2026-01-23 14:28:29 GMT

CSS module scripts landed in Firefox 147, so you can import CSS directly into JavaScript.
Docs:
Import attributes https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/import/with
CSSStyleSheet https://developer.mozilla.org/en-US/docs/Web/API/CSSStyleSheet
https://files.mastodon.social/media_attachments/files/115/944/881/429/553/149/original/7d8c7fc4b8b4eed6.mp4

2026-01-15 12:20:28 GMT

The Navigation API is newly baseline! The web now has sensible, low-level routing for navigations.
https://developer.mozilla.org/en-US/docs/Web/API/Navigation_API
https://files.mastodon.social/media_attachments/files/115/899/077/652/747/471/original/34c0fece654b2127.mp4

2026-01-08 14:32:22 GMT

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Anyway, Firefox 147 is out next week, and it includes a pretty big drop of web platform features which I'm looking forward to presenting! Although, the winter 'ill' seems to have finally caught up with me. Let's see if I have a voice left for the recordings.

2026-01-08 14:32:05 GMT

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This account is about web platform features and DevTools in Firefox. I only got personally involved in the AI kill switch because of previous feedback from many of you here.
I know many of you wanted, instead, a broader referendum on 'AI' features in Firefox. However, I'm not personally in a position to action results of such a poll. Whereas I was confident I could do something about the results of the poll I ran, which is why I ran it.

2026-01-08 14:31:13 GMT

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Thank you everyone who responded to this.
For context: I saw mocks of the kill switch where translation was included, but it lacked the ability to enable the kill switch but still enable particular features (such as translation).
The results of this poll helped me successfully push for more granular control in addition to the single AI kill switch. So again, thank you for that.

2026-01-07 15:42:52 GMT

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ah, I thought 🤷 was well understood to mean "I don't know/care, I just want to see the results". It's pretty commonly used, but clearly not commonly enough. Sorry!

2026-01-06 17:21:57 GMT

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no external service is used. I'm not sure on the resources used for training, but it's useful to know that would factor into your decision. The project is here https://github.com/mozilla/translations

2026-01-06 17:08:04 GMT

Firefox uses on-device downloaded-on-demand ML models for privacy-preserving translation.
They're not LLMs. They're trained on open data.
Should translation be disabled if the AI 'kill switch' is active?

2025-12-19 15:17:24 GMT

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that sounds reasonable to me. Since Firefox is fully open source, you can follow along with the development in places like https://bugzilla.mozilla.org/show_bug.cgi?id=2005800

2025-12-19 15:11:59 GMT

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sounds like the kill switch will be ideal for your use-case

2025-12-19 15:04:19 GMT

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how have those features surfaced in the browser UX for you?

2025-12-19 13:11:40 GMT

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yes. The features are opt-in (but some disagree on what that means), whereas the kill switch is an unambiguous "never offer me this stuff ever"

2025-12-18 13:39:01 GMT

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which features have you personally experienced this with in Firefox?

2025-12-18 12:16:28 GMT

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Just be glad this thread wasn't a long-ass video. It almost was.

2025-12-18 12:12:08 GMT

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I hope we can (re)gain your trust here.
I don't personally work on this stuff, but I'll try hard to answer any questions you have.
And other than that, I'll get back in my lane, and stick to web platform stuff.
- Jake (@npub1dpj…e0jl)

2025-12-18 12:11:37 GMT

- reply

I'm not asking for faith in our direction - the thing I love about the Firefox community is how open, honest, and technical it is.
But I do ask that you don't have the opposite of faith. Like, try not to be determined that we're going to do the wrong thing here.
…

2025-12-18 12:11:29 GMT

- reply

All AI features will also be opt-in. I think there are some grey areas in what 'opt-in' means to different people (e.g. is a new toolbar button opt-in?), but the kill switch will absolutely remove all that stuff, and never show it in future. That's unambiguous.
…

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.
…

2025-12-16 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

2025-12-09 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