Summary: Firefox cannot tolerate being downgraded a major version, the behavior gets all whacky.[1] Note, the problem does not occur with new clean installs (unless you preserve /home), just upgrades.

Detail: Since the ensuing behavior is indistinguishable from buggy behavior, we should have a release criterion ensuring Fedora beta and final ship a version of Firefox equal to or newer than what's available in the two current releases. I think even if it is "a beta" this is way too much horkage to subject beta testers to. They are expecting bugs, but this is not a bug, it's a bad procedure to compel users (without a way to opt out) to downgrade and in effect get a busted web browser experience on upgrade.

Related bugs: ship FF 97 in Fedora beta https://bugzilla.redhat.com/show_bug.cgi?id=2057193 ship FF 99 in Fedora final https://bugzilla.redhat.com/show_bug.cgi?id=2056661

Contra argument: There is a "Default application functionality" final release criterion, it requires a basic functionality test, and includes the web browser. It surely applies here, because the browser is broken for many web sites. As for beta, well it's a beta.

(It's the best contrary argument I could make. I think the "it's a beta! weee!" is not compelling. Plus, it's significantly incompatible with the catch all beta criterion "Bug hinders execution of required Beta test plans or dramatically reduces test coverage" because we just get a bunch of bogus "it's broken" reports from unwitting users who upgrade at beta, ostensibly to test, and then get bitten by this.)

Proposed language:

A. Release-blocking desktops must ship a version of Firefox [default web browser] equal to, or newer than, the version available with both current Fedora releases. B. Release-blocking desktops must ship a version of Firefox [default web browser] that avoids it being downgraded when performing a system upgrade.

[1] https://bugzilla.redhat.com/show_bug.cgi?id=2057193#c6