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...

Firefox 154 release notes for developers (Stable) - Mozilla | MDN

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

developer.mozilla.org

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

Découvrez le bénévolat en traduction — Paris Web

L’interface d’un logiciel, l’assistance et la documentation pour le développement en langue française sont importantes pour toute personne, avec ou sans compétences techniques. Chez Mozilla, la …

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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:

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...

Firefox 152 release notes for developers (Beta) - Mozilla | MDN

This article provides information about the changes in Firefox 152 that affect developers. Firefox 152 is the current Beta version of Firefox and ships on June 16, 2026.

developer.mozilla.org

🆕 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 No more outdated guesses from training data.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/...

CSS scroll snap - CSS | MDN

The CSS scroll snap module provides properties that let you control the panning and scrolling behavior by defining snap positions. Content can be snapped into position as the user scrolls overflowing content within a scroll container, providing paging and scroll positioning.

developer.mozilla.org

📬 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/...