@MozDevNet

The official MDN Web Docs account. We deliver the best web docs around.

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developer.mozilla.org
Joined March 2013
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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/…
MDN's browser compatibility table for the HTML popover attribute. Its columns cover desktop and mobile browsers, showing which versions support the attribute and its "hint" value. A "Settings" button sits above the table.

ALT MDN's browser compatibility table for the HTML popover attribute. Its columns cover desktop and mobile browsers, showing which versions support the attribute and its "hint" value. A "Settings" button sits above the table.

The Browser compatibility settings dialog on MDN. Browsers appear as chips grouped under Desktop, Mobile, Server and XR, and each one can be added to or removed from the table.

ALT The Browser compatibility settings dialog on MDN. Browsers appear as chips grouped under Desktop, Mobile, Server and XR, and each one can be added to or removed from the table.

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What should we ship in 2027? Rank your favourite features & create your wishlist: interop-rank.fxdx.dev/
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JPEG XL vs AVIF for web use-cases. @jaffathecake 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/2026/jpeg-…
Title “JPEG XL vs AVIF” over a grid of six images: a red panda, a racing car, a cartoon cat, a neon “Senna” sign with cats, people holding phones, and a weasel.

ALT Title “JPEG XL vs AVIF” over a grid of six images: a red panda, a racing car, a cartoon cat, a neon “Senna” sign with cats, people holding phones, and a weasel.

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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/…

Firefox 158 release notes for developers (Stable) - Mozilla | MDN

This article provides information about the changes in Firefox 158 that affect developers. Firefox 158 was released on October 13, 2026.

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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/

2027 Web Platform Feature Ranking

Rank the Interop 2027 features you care most about

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Firefox 157 has landed, and includes a couple of useful CSS features: 🎉 at-rule() in @supports - limit rules to browsers that support a given at-rule. 🎉 overscroll-behavior: chain - allow chained scrolling without overscroll effects. …And more! developer.mozilla.org/en-US/…

Firefox 157 release notes for developers - Mozilla | MDN

This article provides information about the changes in Firefox 157 that affect developers. Firefox 157 was released on September 29, 2026.

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

Firefox 155 release notes for developers - Mozilla | MDN

This article provides information about the changes in Firefox 155 that affect developers. Firefox 155 was released on September 1, 2026.

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CSS text-box is newly baseline, and it's solves a common text layout issue. Here's how it works: instagram.com/reel/DcORXuGFN…

Firefox for Web Developers (@firefoxwebdevs) • Instagram reel

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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/…

Firefox 154 release notes for developers - Mozilla | MDN

This article provides information about the changes in Firefox 154 that affect developers. Firefox 154 was released on August 18, 2026.

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JS promise integration for WebAssembly landed in Firefox 153, making it easier to work with asynchronous calls from Wasm. Here's how it works:
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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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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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CSS field-sizing is newly baseline, meaning you can make various form fields size to their contents, without needing JavaScript.
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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/…

Firefox 152 release notes for developers - Mozilla | MDN

This article provides information about the changes in Firefox 152 that affect developers. Firefox 152 was released on June 16, 2026.

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🆕 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/…
A headline Introducing MDN MCP server above a terminal window titled Light-dark CSS function for images, showing a prompt asking how to use the light-dark() CSS function for images and which browsers support it, with a note that the mdn tool was called 4 times, followed by an answer explaining that light-dark() takes two image values and works anywhere an image is accepted. The MDN logo appears on the right.

ALT A headline Introducing MDN MCP server above a terminal window titled Light-dark CSS function for images, showing a prompt asking how to use the light-dark() CSS function for images and which browsers support it, with a note that the mdn tool was called 4 times, followed by an answer explaining that light-dark() takes two image values and works anywhere an image is accepted. The MDN logo appears on the right.

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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:
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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 👇
A colorful infographic titled “MDN HTTP Code Cheatsheet with Emojis.” It categorizes HTTP status codes using emoji-enhanced lists grouped by status code classes.

ALT A colorful infographic titled “MDN HTTP Code Cheatsheet with Emojis.” It categorizes HTTP status codes using emoji-enhanced lists grouped by status code classes.

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🦊 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/…
Firefox 150 release notes feature a minimalist design with soft colors, highlighting new capabilities for web extensions.

ALT Firefox 150 release notes feature a minimalist design with soft colors, highlighting new capabilities for web extensions.

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🦊 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/…
Firefox 150 release notes with a smooth background design featuring soft waves in pastel colors.

ALT Firefox 150 release notes with a smooth background design featuring soft waves in pastel colors.

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