

It was collapsed for me at first, and buried under a lot of other comments, but a workaround is mentioned here. Unfortunately, that didn’t seem to work for me, but deleting the Flatpak and deleting all associated data, and then reinstalling it, I think did the trick.
Although it does now show this warning, which doesn’t sound great.
Edit: actually, I think that was the reason I concluded the first workaround didn’t work, but looking at that URL, this might just have been introduced in Firefox 128, which is newer than the old version of Tor was based on. So it looks like both worked.
Which Mozilla projects started out as free and are now non-free, i.e. no longer under an open source (or even viral open source) licence?