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.https://waldmeister.eu/profile/webdevs.firefox.comhttps://waldmeister.eu/profile/webdevs.firefox.com/post/3mrmxmyt3rk2gI made an accessibility error in one of my recent videos, and I want you to learn from my mistake: (sorry, yet another YT link - bsky video uploads are still broken) https://www.youtube.com/shorts/hPrZiRSRCE427 Jul 2026 13:07 +0000at://did:plc:6jsvyhtxrkb4d2wrlwd2avmm/app.bsky.feed.post/3mrmxmyt3rk2ghttps://waldmeister.eu/profile/webdevs.firefox.com/post/3mrcxegis6s2gA little dive into web standards… Why changes were made to popover="hint", and why diversity in browser engines is important: (sorry again for the YT link - video uploads are still broken on bsky) https://youtube.com/shorts/9LDmdQ6eKJA?feature=share23 Jul 2026 13:35 +0000at://did:plc:6jsvyhtxrkb4d2wrlwd2avmm/app.bsky.feed.post/3mrcxegis6s2ghttps://waldmeister.eu/profile/webdevs.firefox.com/post/3mragwu63d227popover="hint" landed in Firefox 153. Here's how it differs from regular popovers: https://youtube.com/shorts/HWetxbInaVc?feature=share (sorry for the YouTube link, it seems like video uploads are broken on bsky today)22 Jul 2026 13:36 +0000at://did:plc:6jsvyhtxrkb4d2wrlwd2avmm/app.bsky.feed.post/3mragwu63d227https://waldmeister.eu/profile/webdevs.firefox.com/post/3mr7w6owkjs27JS declarations in conditionals is being discussed at TC39 again. The tricky detail is, how should the "else" block be handled? I think Rust has the right answer here: https://bsky.app/profile/webdevs.firefox.com/post/3m7zwmhedij2m [contains quote post or other embedded content]22 Jul 2026 08:36 +0000at://did:plc:6jsvyhtxrkb4d2wrlwd2avmm/app.bsky.feed.post/3mr7w6owkjs27https://waldmeister.eu/profile/webdevs.firefox.com/post/3mr5sdnr5pe2rFirefox 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/15321 Jul 2026 12:22 +0000at://did:plc:6jsvyhtxrkb4d2wrlwd2avmm/app.bsky.feed.post/3mr5sdnr5pe2rhttps://waldmeister.eu/profile/webdevs.firefox.com/post/3mqqrwetd5p2uSomeone said our Instagram page looks like "the world's most boring game of Guess Who" 😭 https://www.instagram.com/firefoxwebdevs/reels/16 Jul 2026 08:10 +0000at://did:plc:6jsvyhtxrkb4d2wrlwd2avmm/app.bsky.feed.post/3mqqrwetd5p2uhttps://waldmeister.eu/profile/webdevs.firefox.com/post/3mqoocndsms25Ohhhh this has just been added to WebKit https://bugs.webkit.org/show_bug.cgi?id=319178 [contains quote post or other embedded content]15 Jul 2026 12:00 +0000at://did:plc:6jsvyhtxrkb4d2wrlwd2avmm/app.bsky.feed.post/3mqoocndsms25https://waldmeister.eu/profile/webdevs.firefox.com/post/3mq7u7qem5s2qNotification actions landed in Firefox 152, allowing you to add quick action buttons to your notifications. Here's how they work:09 Jul 2026 14:36 +0000at://did:plc:6jsvyhtxrkb4d2wrlwd2avmm/app.bsky.feed.post/3mq7u7qem5s2qhttps://waldmeister.eu/profile/webdevs.firefox.com/post/3moikk2krss2nCSS field-sizing is newly baseline, meaning you can make various form fields size to their contents, without needing JavaScript.17 Jun 2026 14:46 +0000at://did:plc:6jsvyhtxrkb4d2wrlwd2avmm/app.bsky.feed.post/3moikk2krss2nhttps://waldmeister.eu/profile/webdevs.firefox.com/post/3mofyd2u6wc2aFirefox 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/15216 Jun 2026 14:15 +0000at://did:plc:6jsvyhtxrkb4d2wrlwd2avmm/app.bsky.feed.post/3mofyd2u6wc2ahttps://waldmeister.eu/profile/webdevs.firefox.com/post/3modhqde42j2aIf 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: savearoundtrip.com https://savearoundtrip.com/15 Jun 2026 14:13 +0000at://did:plc:6jsvyhtxrkb4d2wrlwd2avmm/app.bsky.feed.post/3modhqde42j2ahttps://waldmeister.eu/profile/webdevs.firefox.com/post/3mncp42h7ik2bEver struggled to get heading tags right in includes/components? headingoffset could be the answer…02 Jun 2026 13:26 +0000at://did:plc:6jsvyhtxrkb4d2wrlwd2avmm/app.bsky.feed.post/3mncp42h7ik2bhttps://waldmeister.eu/profile/webdevs.firefox.com/post/3mnaax3jnmm2aWe'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/01 Jun 2026 14:08 +0000at://did:plc:6jsvyhtxrkb4d2wrlwd2avmm/app.bsky.feed.post/3mnaax3jnmm2ahttps://waldmeister.eu/profile/webdevs.firefox.com/post/3mmwapqehrf2hThe 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:28 May 2026 14:37 +0000at://did:plc:6jsvyhtxrkb4d2wrlwd2avmm/app.bsky.feed.post/3mmwapqehrf2hhttps://waldmeister.eu/profile/webdevs.firefox.com/post/3mmquowbod22nWhich of the following three CSS features would you prefer Firefox to support first? ❤️ your favorite in the thread:26 May 2026 11:19 +0000at://did:plc:6jsvyhtxrkb4d2wrlwd2avmm/app.bsky.feed.post/3mmquowbod22nhttps://waldmeister.eu/profile/webdevs.firefox.com/post/3mmf3yyot5k2vWeb 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/21 May 2026 18:58 +0000at://did:plc:6jsvyhtxrkb4d2wrlwd2avmm/app.bsky.feed.post/3mmf3yyot5k2vhttps://waldmeister.eu/profile/webdevs.firefox.com/post/3mmbyn7qc2m26CSS style() queries landed in Firefox 151 making them newly available across engines. Here's how they work:20 May 2026 13:19 +0000at://did:plc:6jsvyhtxrkb4d2wrlwd2avmm/app.bsky.feed.post/3mmbyn7qc2m26https://waldmeister.eu/profile/webdevs.firefox.com/post/3mm7h5hjxyy2yFirefox 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/15119 May 2026 13:01 +0000at://did:plc:6jsvyhtxrkb4d2wrlwd2avmm/app.bsky.feed.post/3mm7h5hjxyy2yhttps://waldmeister.eu/profile/webdevs.firefox.com/post/3mm53xi3po22eChrome shipped an LLM Prompt API to the web platform. At Mozilla, we oppose this API. Here's why:18 May 2026 14:35 +0000at://did:plc:6jsvyhtxrkb4d2wrlwd2avmm/app.bsky.feed.post/3mm53xi3po22ehttps://waldmeister.eu/profile/webdevs.firefox.com/post/3mlbmbqbmva2vRecently, 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/07 May 2026 16:13 +0000at://did:plc:6jsvyhtxrkb4d2wrlwd2avmm/app.bsky.feed.post/3mlbmbqbmva2vhttps://waldmeister.eu/profile/webdevs.firefox.com/post/3mkpb2lg5sm2oChrome 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-434798831330 Apr 2026 09:04 +0000at://did:plc:6jsvyhtxrkb4d2wrlwd2avmm/app.bsky.feed.post/3mkpb2lg5sm2ohttps://waldmeister.eu/profile/webdevs.firefox.com/post/3mki5oy2ecg2nCSS's light-dark() now accepts images, making it simpler to define alternate values for a dark color scheme. Here's how it works:27 Apr 2026 13:15 +0000at://did:plc:6jsvyhtxrkb4d2wrlwd2avmm/app.bsky.feed.post/3mki5oy2ecg2nhttps://waldmeister.eu/profile/webdevs.firefox.com/post/3mk63jssnx42lsizes="auto" landed in Firefox 150, making responsive images simpler and more reliable. Here's when you can use it, and how…23 Apr 2026 13:10 +0000at://did:plc:6jsvyhtxrkb4d2wrlwd2avmm/app.bsky.feed.post/3mk63jssnx42lhttps://waldmeister.eu/profile/webdevs.firefox.com/post/3mjyto2qmkh2yFirefox 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/15021 Apr 2026 11:06 +0000at://did:plc:6jsvyhtxrkb4d2wrlwd2avmm/app.bsky.feed.post/3mjyto2qmkh2yhttps://waldmeister.eu/profile/webdevs.firefox.com/post/3mjmjbxk3sh2pmap.getOrInsertComputed is newly baseline! It's a small feature, but I've found it pretty useful. Here's how it works:16 Apr 2026 13:28 +0000at://did:plc:6jsvyhtxrkb4d2wrlwd2avmm/app.bsky.feed.post/3mjmjbxk3sh2phttps://waldmeister.eu/profile/webdevs.firefox.com/post/3mjjplmb7j62pA 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=split15 Apr 2026 10:43 +0000at://did:plc:6jsvyhtxrkb4d2wrlwd2avmm/app.bsky.feed.post/3mjjplmb7j62phttps://waldmeister.eu/profile/webdevs.firefox.com/post/3mjhntq3tbx2dCSS contrast-color is newly baseline, but it falls short in some areas. Here's how it works, and what to look out for:14 Apr 2026 15:06 +0000at://did:plc:6jsvyhtxrkb4d2wrlwd2avmm/app.bsky.feed.post/3mjhntq3tbx2dhttps://waldmeister.eu/profile/webdevs.firefox.com/post/3mjhntq3tbx2dCSS contrast-color is newly baseline, but it falls short in some areas. Here's how it works, and what to look out for:14 Apr 2026 15:06 +0000at://did:plc:6jsvyhtxrkb4d2wrlwd2avmm/app.bsky.feed.post/3mjhntq3tbx2d