It seems like my entire profile (about:profiles) got switched out several times with a brand new one. Exact same symptoms as you - bookmarks, custom UI tweaks, extensions, etc. all gone (basically consistent with creating a new profile yourself). For a regular user, I think that only needs to happen once for them to uninstall and never come back.

Most of the time I've been able to restore it to my old profile, but one time a file was corrupted and I had to start from scratch again. It happened before the extension signing fiasco, and those two things combined led me to explore new options (Vivaldi, Chromium, etc.) although those didn't pan out for me so here I am, still on Firefox and crossing my fingers hoping it won't happen again.

Perhaps relevant: I do have Nightly and Developer Edition installed alongside the regular version. I used to use Nightly as my daily driver, but switched to the regular version after the first time my profile got messed up.