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

NEW (nobody) in Core - CSS Parsing and Computation. Last updated 2026-08-20.

With the `progress()` function in CSS we've got a new way to calculate the size for type based on the viewport without problems of the past.

The progress() CSS function returns a <number> value representing the position of one value (the progress value) relative to two other values (the progress start and end values).

GitHub is where people build software. More than 150 million people use GitHub to discover, fork, and contribute to over 420 million projects.

You saw Kit, and that was it.    Made by Everybody.World, this tee is for the ones who get it — the quiet joy of spotting Kit out in the wild.   It’s soft, relaxed and made to wear on repeat, with jus...

web-platform-tests Interop project. Contribute to web-platform-tests/interop development by creating an account on GitHub.

The attr() CSS function is used to retrieve the value of an attribute of the selected element and use it in a property value, similar to how the var() function substitutes a custom property value. It…

NEW (nobody) in Core - CSS Parsing and Computation. Last updated 2026-09-03.

Request for Mozilla Position on an Emerging Web Specification Specification Title: Federated Credential Management API Specification or proposal URL: explainer specification TPAC2021 presentation (...

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

The sibling-index() CSS function returns an integer representing the position of the current element in the DOM tree relative to all its sibling elements. The returned value is the index number of…

A JPEG XL decoder is heading for Firefox 157! Here's how we're shipping it safely…

As of Firefox 157 I intend to turn JPEG XL decoding on by default on all platforms. It has been developed behind image.jxl.enabled, which today is on by default on Nightly only, and has had a Firefox…

When the line-height is smaller than the font's ascent/descent, line boxes can have negative leading. If text-box-trim is applied to a block using a taller edge metric, does it remove this negative...

NEW (nobody) in Core - Layout. Last updated 2026-08-17.