Nostr notes by Firefox for Web Developers

Major versions of Firefox now land every two weeks, so Firefox ...

2026-09-01T13:15:06Z

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()
🎉 CSS alpha()
🎉 Promise.allKeyed() and allSettledKeyed()
🎉 Wasm wide arithmetic
🎉 Lots of new WebTransport stuff

…And more!

https://developer.mozilla.org/en-US/docs/Mozilla/Firefox/Releases/155

CSS sibling-count() and sibling-index() are newly available ...

2026-08-25T13:03:43Z

CSS sibling-count() and sibling-index() are newly available across engines! Here's how they work:

And the full docs on MDN: ...

2026-08-25T13:03:43Z

In reply to nevent1q…uwx9
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And the full docs on MDN: https://developer.mozilla.org/en-US/docs/Web/CSS/Reference/Values/sibling-index

the Safari implementation is missing big features like ...

2026-08-24T16:35:56Z

In reply to nevent1q…l80f
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the Safari implementation is missing big features like progressive rendering. More details here https://hacks.mozilla.org/2026/08/intent-to-ship-jpeg-xl/

Chrome also has an Intent to Ship, so support should land in both ...

2026-08-24T11:50:49Z

In reply to nevent1q…r9x3
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Chrome also has an Intent to Ship, so support should land in both browsers within a week of each other https://groups.google.com/a/chromium.org/g/blink-dev/c/-gDojQbDPRI

In a JPEG XL compatible browser (like Firefox Nightly), test how ...

2026-08-24T11:49:04Z

In reply to nevent1q…2cld
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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

Intent to ship: JPEG XL! This will be on-by-default in Firefox ...

2026-08-24T11:49:03Z

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.

https://groups.google.com/a/mozilla.org/g/dev-platform/c/3YMV4MS34KA

What should happen with text-box-trim and margin-trim when it ...

2026-08-20T13:04:19Z

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 ...

2026-08-19T13:15:16Z

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 ...

2026-08-18T13:15:05Z

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

JS promise integration for WebAssembly landed in Firefox 153, ...

2026-08-04T12:12:57Z

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 ...

2026-07-30T12:38:48Z

JS text imports landed in Firefox 153, making it the first browser to support this feature. Here's how it works:

RE: https://mastodon.social/@FirefoxOfficial/116958818480299400 ...

2026-07-21T16:19:04Z

RE: https://mastodon.social/@FirefoxOfficial/116958818480299400

The official Firefox account is back on fedi!

(I mean, this one is official too, but… you know what I mean)

quoting
note1duq…d0ux

Hi, fediverse. Firefox 153 has landed with Tab Groups on Android, Quick Answers rolling out on iOS, a preview of native Containers, and HDR support on Windows.

Let us know what you try out: https://www.firefox.com/en-US/firefox/153.0/releasenotes/

Firefox 153 just landed, and comes with web platform features ...

2026-07-21T12:22:22Z

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

Firefox 152 landed today, and includes web platform features ...

2026-06-16T14:15:05Z

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

If your content is served over HTTP/3, make sure your DNS record ...

2026-06-15T14:20:18Z

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/

Ever struggled to get heading tags right in includes/components? ...

2026-06-02T13:23:20Z

Ever struggled to get heading tags right in includes/components? headingoffset could be the answer…

We're experimenting with a way to visualize session history ...

2026-06-01T14:08:01Z

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/

The Web Serial API landed in Firefox 151, allowing you to connect ...

2026-05-28T14:37:49Z

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:

CSS style() queries landed in Firefox 151 making them newly ...

2026-05-20T13:18:58Z

CSS style() queries landed in Firefox 151 making them newly available across engines. Here's how they work:

Chrome shipped an LLM Prompt API to the web platform. At Mozilla, ...

2026-05-18T14:28:12Z

Chrome shipped an LLM Prompt API to the web platform. At Mozilla, we oppose this API. Here's why:

unfortunately it isn't so mysterious, it's a consequence ...

2026-05-06T10:25:34Z

In reply to nevent1q…s8u5
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unfortunately it isn't so mysterious, it's a consequence of real-world usage.

There's even a standard for some of this stuff https://compat.spec.whatwg.org/. It's sad that it's this way, but it's required to make a browser that works with in-the-wild content.

this is happening because the site tests for support of ...

2026-05-03T09:03:01Z

In reply to nevent1q…vkxl
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this is happening because the site tests for support of `::-webkit-scrollbar`, but assumes that `::-webkit-scrollbar-button` would also be supported, and that isn't true in 152.

thanks! I've filed ...

2026-05-03T08:54:55Z

In reply to nevent1q…6enx
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thanks! I've filed https://bugzilla.mozilla.org/show_bug.cgi?id=2036615

is this error reproducible? Can you create a demo?

2026-05-03T08:14:17Z

In reply to nevent1q…8c5u
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is this error reproducible? Can you create a demo?

Chrome looks set to ship an LLM Prompt API to the web platform. ...

2026-04-30T09:04:38Z

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

hasUAVisualTransition landed in Firefox 149, making it available ...

2026-03-26T14:38:35Z

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:

CSS shape() landed in Firefox 148. It's similar to path(), ...

2026-03-02T15:06:52Z

CSS shape() landed in Firefox 148. It's similar to path(), but allows the full expressiveness of CSS…

You can throw away innerHTML and replace it with the new ...

2026-02-25T12:07:54Z

You can throw away innerHTML and replace it with the new setHTML(), which has a built-in sanitizer. Here's how it works:

HTML might be getting a new type of tag, which… hasn't ...

2026-02-16T14:45:37Z

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

If you had to pick _one_, which web platform feature would you ...

2026-02-13T09:34:51Z

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

here's the help page, so you can judge for yourself ...

2026-02-03T12:34:00Z

In reply to nevent1q…c9c6
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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 😀

I don't think it's particularly unusual to offer features ...

2026-02-03T12:19:36Z

In reply to nevent1q…5rt5
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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.

fwiw, the individual features are, to some extent, opt in. As in, ...

2026-02-03T12:07:23Z

In reply to nevent1q…03ql
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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.

translation is valuable for reading parts of the web that ...

2026-02-02T22:58:16Z

In reply to nevent1q…5u4s
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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.

Sad to see you go. Fwiw, LibreWolf has translation very similar ...

2026-02-02T22:44:34Z

In reply to nevent1q…jpcx
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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.

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

2026-02-02T19:21:51Z

In reply to nevent1q…ay63
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I'm not sure what we can do to convince you other than hold the promise over time.

AI Controls (formally 'kill switch') are landing in ...

2026-02-02T17:04:39Z

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/

CSS module scripts landed in Firefox 147, so you can import CSS ...

2026-01-23T14:28:29Z

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

The Navigation API is newly baseline! The web now has sensible, ...

2026-01-15T12:20:28Z

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

Anyway, Firefox 147 is out next week, and it includes a pretty ...

2026-01-08T14:32:22Z

In reply to nevent1q…wcas
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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.

This account is about web platform features and DevTools in ...

2026-01-08T14:32:05Z

In reply to nevent1q…3xlp
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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.

Thank you everyone who responded to this. For context: I saw ...

2026-01-08T14:31:13Z

In reply to nevent1q…xydg
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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.

ah, I thought 🤷 was well understood to mean "I don't ...

2026-01-07T15:42:52Z

In reply to nevent1q…z4lg
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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!

no external service is used. I'm not sure on the resources ...

2026-01-06T17:21:57Z

In reply to nevent1q…kwjn
_________________________

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

Firefox uses on-device downloaded-on-demand ML models for ...

2026-01-06T17:08:04Z

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?

that sounds reasonable to me. Since Firefox is fully open source, ...

2025-12-19T15:17:24Z

In reply to nevent1q…3n56
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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

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

2025-12-19T15:11:59Z

In reply to nevent1q…4j9z
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sounds like the kill switch will be ideal for your use-case

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

2025-12-19T15:04:19Z

In reply to nevent1q…mcvy
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how have those features surfaced in the browser UX for you?

yes. The features are opt-in (but some disagree on what that ...

2025-12-19T13:11:40Z

In reply to nevent1q…que4
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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"

which features have you personally experienced this with in ...

2025-12-18T13:39:01Z

In reply to nevent1q…2t5y
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which features have you personally experienced this with in Firefox?

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

2025-12-18T12:16:28Z

In reply to nevent1q…nyhp
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Just be glad this thread wasn't a long-ass video. It almost was.

I hope we can (re)gain your trust here. I don't personally ...

2025-12-18T12:12:08Z

In reply to nevent1q…dvn0
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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 (Jake Archibald (npub1dpj…e0jl))

I'm not asking for faith in our direction - the thing I love ...

2025-12-18T12:11:37Z

In reply to nevent1q…8k3t
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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.

…

All AI features will also be opt-in. I think there are some grey ...

2025-12-18T12:11:29Z

In reply to nevent1q…z6cq
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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.

…

Something that hasn't been made clear: Firefox will have an ...

2025-12-18T12:11:21Z

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.

…

HTML invoker commands are newly baseline! Here's how they ...

2025-12-16T16:24:41Z

HTML invoker commands are newly baseline! Here's how they work…

CSS @scope has landed in Firefox 146, making it a new baseline ...

2025-12-09T15:57:54Z

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