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

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

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  A little dive into web standards… Why changes were made to popover="hint", and why diversity in browser engines is important:

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  popover="hint" landed in Firefox 153. Here's how it differs from regular popovers:

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  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)

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  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?

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  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.

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  Notification actions landed in Firefox 152, allowing you to add quick action buttons to your notifications. Here's how they work:

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  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/

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

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  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

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

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  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/

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  Recently, we fixed an unprecedented number of latent security bugs in Firefox identified by Claude Mythos Preview. Here's how we approached this work, what we found, and what we learned: https://hacks.mozilla.org/2026/05/behind-the-scenes-hardening-firefox/

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  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

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  CSS's light-dark() now accepts images, making it simpler to define alternate values for a dark color scheme. Here's how it works:

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  sizes="auto" landed in Firefox 150, making responsive images simpler and more reliable. Here's when you can use it, and how…

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  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

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  HTML hidden=until-found and auto-opening <details> is newly baseline… or is it? Here's how it works, and issues to watch out for:

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  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. …

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  @stefanfrede no, that isn't intentional. Can you confirm which version of Firefox you're seeing the change in?

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  @stefanfrede https://bugzilla.mozilla.org/show_bug.cgi?id=2026109 here it is. The fix will be uplifted to 149 soon.

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  A common mistake with a 'subtree' MutationObserver is assuming addedNodes includes all newly connected nodes, but it doesn't include preexisting children of the added nodes https://codepen.io/editor/jaffathecake/pen/019d90a5-98e5-7d08-b85f-630c9257cfad?console=true&file=%2Fscript.js&orientation=left&show=split

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  map.getOrInsertComputed is newly baseline! It's a small feature, but I've found it pretty useful. Here's how it works. Full docs and polyfills on MDN https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/WeakMap/getOrInsertComputed

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  CSS contrast-color is newly baseline, but it falls short in some areas. Here's how it works, and what to look out for:

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  Can you tell CSS from BS? I tried, and it's hard. https://indieweb.social/@keithamus/116328410312008711

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  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/

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  Firefox 149 is out now, and adds bunch of new web platform features, such as: 🎉 The CloseWatcher API 🎉 popover=hint (although I'm concerned about the spec'd behaviour) 🎉 hasUAVisualTransition on PopStateEvent 🎉 font-family: math 🎉 The CSP reporting API And more! https://developer.mozilla.org/en-US/docs/Mozilla/Firefox/Releases/149

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  The CloseWatcher API landed in Firefox 149, making it easy to listen for platform-specific 'dismiss' signals. Here's how it works:

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  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: