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• Post #4240824

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

• Post #4074131

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

• Post #4013119

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

• Post #3992443

  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)

• Post #3891815

  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?

• Post #3805738

  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.

• Post #3699521

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

• Post #3326343

  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/

• Post #2856302

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

• Post #2856301

  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

• Post #2856300

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

• Post #2856299

  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/

• Post #2354395

  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/

• Post #1802354

  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

• Post #1754472

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

• Post #1651923

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

• Post #1520908

  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

• Post #1505664

  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:

• Post #1390790

  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. …

• Post #1381766

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

• Post #1381765

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

• Post #1381764

  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

• Post #1381748

  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

• Post #1180448

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

• Post #924133

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

• Post #831129

  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/

• Post #831128

  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

• Post #831126

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

• Post #831124

  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:

• Post #670956

  JavaScript Iterator․zip landed in Firefox 148, making it simple to loop over multiple things at the same time. Here's how it works: