Firefox for Web Developers

@firefoxwebdevs
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Official Firefox account for people who build on the web. Learn about the things we're working on to grow and improve the web platform.
If you want to experience the gross 3d transition first hand: https://simple-vt-demos.jakearchibald.com/gross-cube-transition-shaded/
Demo

hasUAVisualTransition landed in Firefox 149, making it available across all major engines. As well as having a very catchy name, it lets you avoid doubling up on page transitions. Here's how it works:
And, of course, the full documentation on MDN https://developer.mozilla.org/en-US/docs/Web/API/CloseWatcher
CloseWatcher - Web APIs | MDN

The CloseWatcher interface allows a custom UI component with open and close semantics to respond to device-specific close actions in the same way as a built-in component.

MDN Web Docs
The CloseWatcher API landed in Firefox 149, making it easy to listen for platform-specific 'dismiss' signals. Here's how it works:
In terms of popover=hint, I dug into it when scripting a video, and… I can't make sense of the behaviour at all. Here's my investigation so far if you want to follow along: https://github.com/whatwg/html/issues/12304 & https://github.com/whatwg/html/issues/12305

Firefox 149 is out now, and adds bunch of new web platform features, such as:

πŸŽ‰ The CloseWatcher API
πŸŽ‰ popover=hint (although I'm concerned about the spec'd behaviour)
πŸŽ‰ hasUAVisualTransition on PopStateEvent
πŸŽ‰ font-family: math
πŸŽ‰ The CSP reporting API

And more!

https://developer.mozilla.org/en-US/docs/Mozilla/Firefox/Releases/149

Firefox 149 release notes for developers (Stable) - Mozilla | MDN

This article provides information about the changes in Firefox 149 that affect developers. Firefox 149 was released on March 24, 2026.

MDN Web Docs
There are many browsers, but only three widely-used engines. We maintain one of those engines - Gecko. Here's why we feel that browser engine diversity is essential for the future of the web https://blog.mozilla.org/netpolicy/2026/03/23/competition-innovation-and-the-future-of-the-web/
Competition, Innovation, and the Future of the Web – Why Independent Browser Engines Matter – Open Policy & Advocacy

Gecko matters because it ensures there’s an independent voice shaping how the internet evolves. Without Gecko, the landscape would be dominated by Apple and Google alone. Is that really the ...

Open Policy & Advocacy

RE: https://indieweb.social/@keithamus/116204286323408885

Sorry everyone. You're about to spend a ton of time on this.

My score is 0.0028 πŸ’… (although I get different scores on different screens - my best is on my MacBook)

Iterator.zip() - JavaScript | MDN

The Iterator.zip() static method creates a new Iterator object that aggregates elements from multiple iterable objects by yielding arrays containing elements at the same position. It essentially "zips" the input iterables together, allowing simultaneous iteration over them.

MDN Web Docs