New to the web platform in August

Discover some of the interesting features that have landed in stable and beta web browsers during August 2025.

Rachel Andrew

Published: August 29, 2025

Stable browser releases

Chrome 139 and Firefox 142 released to stable during August, this post takes a look at what that means for the web platform.

The URL Pattern API

Firefox 142 supports the URL Pattern API, this makes it much easier to match and parse URLs. This feature is already in Chrome, and in the Safari 26 beta, which should mean we see it in Baseline soon.

Browser Support

  • Chrome: 95.
  • Edge: 95.
  • Firefox: 142.
  • Safari: 26.

Source

Prioritized Task Scheduling

Firefox 142 also supports the Prioritized Task Scheduling API. Support includes Scheduler, TaskController, TaskSignal, TaskPriorityChangeEvent (and the prioritychange event), and the properties Window.scheduler and WorkerGlobalScope.scheduler.

Browser Support

  • Chrome: 94.
  • Edge: 94.
  • Firefox: 142.
  • Safari: not supported.

Source

This means that you can now use scheduler.yield to break up long tasks in both Chrome and Firefox—there's also a polyfill available that can help where it's not supported.

CSS corner shaping

If you've always wanted to be able to create a squircle, you'll be happy to see the new corner-shape property in Chrome 139. This works alongside border-radius, letting you adjust the shape of the corner for the first time.

Browser Support

  • Chrome: 139.
  • Edge: 139.
  • Firefox: not supported.
  • Safari: not supported.

More details and some examples in Understanding CSS corner-shape and the Power of the Superellipse.

CSS custom functions

Also in Chrome 139 are CSS custom functions. These are similar to custom properties, but instead of returning a single, fixed value, they return values based on other custom properties, parameters, and conditionals.

CSS functions are defined using the @function rule, and are part of the CSS Custom Functions and Mixins specification.

Browser Support

  • Chrome: 139.
  • Edge: 139.
  • Firefox: not supported.
  • Safari: not supported. 

@function --negate(--value) {
result: calc(var(--value) * -1);
}

div {
--gap: 1em;
margin-top: --negate(var(--gap));
}

The request-close invoker command

Dialog elements can be closed through a variety of mechanisms, sometimes developers want to have the ability to prevent closure. To achieve this dialogs fire a cancel event. Originally this was only fired using a close request (for example, an ESC key press), recently a requestClose() JavaScript function was added which also fires the cancel event.

The request-close command, now in Chrome 139, brings that new ability to the declarative invoker commands API.

Browser Support

  • Chrome: 139.
  • Edge: 139.
  • Firefox: behind a flag.
  • Safari Technology Preview: supported.

Beta browser releases

Beta browser versions give you a preview of things that will be in the next stable version of the browser. It's a great time to test new features, or removals, that could impact your site before the world gets that release. New betas this month are Firefox 143 and Chrome 140, with Safari 26 beta still ongoing.

Firefox 143 includes the ::details-content pseudo-element, which is included in Interop 2025. This release will make the feature Baseline Newly available. Also included is the CSS text-autospace property. This internationalization feature is helpful if you are displaying Chinese, Japanese, or Korean (CJK) text alongside non-CJK characters. It lets you specify the space applied between these characters.

Chrome 140 includes the source attribute of ToggleEvent, which contains the element that triggered the ToggleEvent to be fired. Also included is font-variation-settings descriptor support in the @font-face rule, along with a number of WebGPU updates.