Firefox browser suddenly fails to load websites, here is the fix

A bizarre bug in Firefox has surfaced which means Firefox users can’t load any websites in the desktop Mac, Windows, and Linux versions of the browser. While the developers are working on a fix for the bug, there is a fix you can apply to work around the issue…

Affected users simply see their tabs spinning forever, never finishing loading to view the page.

The underlying issue preventing pages from loading appears to be a infinite loop bug in Firefox’s HTTP3 implementation. This basically causes the browser process to hang indefinitely.

In particular, the current theory is that one of Firefox’s data analysis services was recently upgraded to an HTTP3-powered backend and the browser is unable to resolve it successfully. The actual implementation bug has been around for a while, but it only surfaced because Firefox tries to connect to data analytics servers almost immediately after launching the app.

Fortunately, very few real websites actually care about HTTP3, with almost everyone still using older standards or providing a fallback. This means that HTTP3 capability is not yet required to browse the modern web. The workaround for the bug then is to simply disable HTTP3 loading in Firefox entirely. To do this:

  1. Open a new Firefox window.
  2. Type about:config in the URL bar. This will open a settings screen.
  3. Look for the ‘network.http.http3.enabled’ setting.
  4. Set this parameter to “false” to disable HTTP3.
  5. Then completely close and restart Firefox.

This workaround applies to all desktop versions of Firefox, so it will work whether you’re on Windows or Mac.

Of course, once the software bug is fixed, you’ll want to go back and re-enable HTTP3 so you can use HTTP3-dependent services in the future.

(The iOS version of Firefox is not affected by the bug because its underlying rendering engine is WebKit, the same as Safari. Indeed, on iOS, Apple does not allow third-party browsers to use their own engines to security reasons).

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