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🆕 Customize MDN's browser compat tables! Press ⚙️ Settings on any compat table to choose which browsers and engines you see, and hide the ones you don't need. Your picks are saved in your browser. Try it 👇 developer.mozilla.org/en-US/docs/W...

JPEG XL is newly available in all major engines, but how does it stack up against other formats?

What should we ship in 2027? Rank your favourite features & create your wishlist: interop-rank.fxdx.dev

JPEG XL vs AVIF for web use-cases. Jake Archibald benchmarked both: AVIF produces smaller lossy files for photos, screenshots, and transparency, while JPEG XL wins at lossless. His default is AVIF 4:4:4 at high effort. #image #performance jakearchibald.com/20...

Firefox 158 landed today! For web devs: 🎉 JPEG XL support, including full progressive rendering. 🎉 'navigate' on notifications, so they can go to a URL without firing events. 🎉 WebGPU's float32-blendable 🎉 WebGL's EXT_polygon_offset_clamp And more! developer.mozilla.org/en-US/docs/M...

What do you want us to work on in 2027? Here's a web app where you can rank the Interop proposals you care about, giving us data we can use to prioritise feature development. interop-rank.fxdx.dev

Firefox 157 has landed, and includes a couple of useful CSS features: 🎉 at-rule() in @supports - lets you limit rules to browsers that support a given at-rule. 🎉 overscroll-behavior: chain - lets scrolling pass up to parent elements, but prevents UA effects like 'bounce' and overscroll. …And more!

When and how CSS custom property values are calculated might not be what you expect, and it has a big impact on your styles…

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() 🎉 Promise.allKeyed() and allSettledKeyed() 🎉 Lots of new WebTransport stuff …And more! developer.mozilla.org/en-US/docs/M...

CSS attr() now works on all properties in Firefox 155. Here's how it works, and how to get the most out of it:

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

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! developer.mozilla.org/en-US/docs/M...

CSS text-box is newly baseline, and it's solves a common text layout issue. Here's how it works:

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 browser to support this feature. Here's how it works:

Atelier #ParisWeb : le 24 septembre, @hellosct1.bsky.social vous expliquera comment participer à la traduction de @firefox.com ou encore la documentation @developer.mozilla.org. www.paris-web.fr/2026/atelier... #traduction #documentation #logicielLibre #communauté

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

CSS field-sizing is newly baseline, meaning you can make various form fields size to their contents, without needing JavaScript.

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

🆕 Introducing the MDN MCP server! Bring MDN's docs and browser compat data straight into your AI agent or IDE for accurate, up-to-date answers about the web platform. No more outdated guesses from training data. Learn more 👇 developer.mozilla.org/en-US/blog/introducing-mdn-mcp-server/

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:

Ever wish HTTP status codes were easier to remember? 🖼️ Check out this MDN cheatsheet that pairs each status code with an emoji to help you visualize what each one means, from 200 OK ✅ to 418 I’m a teapot 🫖 Check it out 👇

🦊 Firefox 150: web extensions can now use the Web Authentication API. Extensions can create and retrieve WebAuthn credentials for any domain covered by their host permissions. Read Now 👇 developer.mozilla.org/en-US/docs/...

🦊 New in Firefox 150: the revert-rule CSS keyword. Make a property behave as if the current rule didn't exist, letting a value from another matching rule take effect instead. Read Now 👇 developer.mozilla.org/en-US/docs/...

🦊 Firefox 150: light-dark() now accepts image values — not just colors. Use it with images and gradients to adapt visuals based on color scheme. background: light-dark(url(light.png), url(dark.png)); Read Now 👇 developer.mozilla.org/en-US/docs/...

🦊 Firefox 150 ships ariaNotify() on Document and Element. Queue text to be announced by a screen reader — a more ergonomic and reliable alternative to ARIA live regions. Read Now 👇 developer.mozilla.org/en-US/docs/...

🦊 Firefox 150: color-mix() now accepts more than two colors at once. Mix any number of colors in a single declaration — no more nesting multiple calls. Read Now 👇 developer.mozilla.org/en-US/docs/...

🦊 Firefox 150: <img sizes="auto"> is now supported. Lazy-loaded images use their calculated layout size to select from srcset — no more duplicating media queries in HTML. Read Now 👇 developer.mozilla.org/en-US/docs/...

Have you heard of CSS Subgrid? 🤔 A grid item can now pass its parent's grid lines to children, so nested elements align perfectly with the outer layout. No more hacky workarounds for aligned nested grids. Learn more 👇 developer.mozilla.org/en-US/docs/...

🆕 The URL Pattern API is Newly Available! Use it to match and extract parts of URLs, no need to reinvent routing logic. Supports literals, wildcards, named groups, and even regex constraints. Learn how it works 👇 developer.mozilla.org/en-US/docs/...

Firefox 150 ships 7 media pseudo-classes: :buffering, :muted, :paused, :playing, :seeking, :stalled, :volume-locked. Style <audio> and <video> elements based on their playback state. Read Now 👇 developer.mozilla.org/en-US/docs/...

Wait for all promises, even the failing ones 🔄 `Promise.allSettled()` waits for every promise to finish, success or failure. ⋅ Returns { status: 'fulfilled', value } or { status: 'rejected', reason } ⋅ Perfect for batch operations Learn more 👇 developer.mozilla.org/en-US/docs/...

✨ :only-child now matches elements with no parent! The :only-child selector has been updated — it can now match elements that have no parent at all, not just sole children. A subtle but useful spec alignment across all major browsers. Learn more 👇 developer.mozilla.org/en-US/docs/...

✨ :only-child now matches elements with no parent! The :only-child selector has been updated — it can now match elements that have no parent at all, not just sole children. A subtle but useful spec alignment across all major browsers. Learn more 👇 developer.mozilla.org/en-US/docs/...

Build smooth scroll experiences with CSS scroll snap 📜 Snap scrollable containers to specific positions — carousels, galleries, and paginated views with zero JavaScript. Learn more 👇 developer.mozilla.org/en-US/docs/...

📬 Check own properties safely with Object.hasOwn() A safer alternative to hasOwnProperty, works even on objects with a null prototype. Baseline since 2022 ✅ Learn more 👇 developer.mozilla.org/en-US/docs/...

Create frosted glass effects in CSS 🪟 backdrop-filter applies visual effects to the content behind an element - blur, brightness, contrast, and more. backdrop-filter: blur(10px) brightness(0.9); No JavaScript. No canvas tricks. Learn more 👇 developer.mozilla.org/en-US/docs/...

The CSS next-sibling combinator (+) selects an element only when it immediately follows another, same parent, no elements between them. img + p { font-weight: bold; } Learn more 👇 developer.mozilla.org/en-US/docs/...

🆕 Document.caretPositionFromPoint() is Newly Available! Give it an (x, y) coordinate and get back the exact DOM node and character offset. Perfect for click-to-edit interfaces. Check it out 👇 developer.mozilla.org/en-US/docs/...

🆕 The Popover API is Baseline, no JavaScript needed Tooltips, dropdowns, and menus with just HTML attributes. ⋅ popover attribute on any element ⋅ popovertarget to wire the trigger ⋅ Accessible by default, no ARIA hacks Learn more 👇 developer.mozilla.org/en-US/docs/...

Better error chaining is finally in JavaScript 🔗 `Error.cause` lets you attach the original error when rethrowing, keeping full context without losing the stack. Learn more 👇 developer.mozilla.org/en-US/docs/...

Speed up rendering with content-visibility: auto ⚡ This CSS property skips rendering off-screen content until needed, giving massive performance wins on long pages. ⋅ Pairs with contain-intrinsic-size ⋅ Zero-effort lazy rendering Learn more 👇 developer.mozilla.org/en-US/docs/...

React to element size changes, not just the window 📐 `ResizeObserver` fires when any element's dimensions change, perfect for responsive components. ⋅ Observe padding box, content box, or border box ⋅ Works with dynamic DOM changes Learn more 👇 developer.mozilla.org/en-US/docs/...

Wait for all promises, even the failing ones 🔄 `Promise.allSettled()` waits for every promise to finish, success or failure. ⋅ Returns { status: 'fulfilled', value } or { status: 'rejected', reason } ⋅ Perfect for batch operations Learn more 👇 developer.mozilla.org/en-US/docs/...

Run non-critical work without blocking the UI 💤 `requestIdleCallback()` schedules tasks during browser idle time. ⚠️ Limited Availability ⋅ Runs only when the main thread is free ⋅ Great for analytics, prefetching, and cleanup Learn more 👇 developer.mozilla.org/en-US/docs/...

JavaScript's date object has been tricky for years, but that is changing. The NEW Temporal API brings, 🌍 Easily handle time zones 📆 Precise date math 🕒 Parse ISO strings without errors ⌛ Durations, date ranges, and more. Start experimenting 👇 developer.mozilla.org/en-US/docs/...

JavaScript now has non-mutating array methods ✨ `toSorted()`, `toReversed()`, `toSpliced()`, and `with()` return new arrays instead of modifying the original. No more [...arr].sort() to avoid side effects. Learn more 👇 developer.mozilla.org/en-US/docs/...

🆕 The URL Pattern API is Newly Available! Use it to match and extract parts of URLs, no need to reinvent routing logic. Supports literals, wildcards, named groups, and even regex constraints. Learn how it works 👇 developer.mozilla.org/en-US/docs/...

Show focus rings only when needed 🎯 :focus-visible applies styles when an element receives focus via keyboard, but not on mouse clicks. Better UX for everyone. Read More 👇 developer.mozilla.org/en-US/docs/...

Transform streaming data on the fly 🔄 TransformStream sits between a readable and writable stream, letting you modify chunks as they pass through. Perfect for encoding, compression, or parsing. Learn more 👇 developer.mozilla.org/en-US/docs/...