Mastodawn

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

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

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Firefox for Web Developers 4h ago

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