The Firefox build on the Fedora repository has some tags assigned to a handful of curated bookmarks. The bookmarks can be removed, but the tags aren’t and can’t (when pressing the Delete key or selecting from the context menu in the ‘library’ view accessed via Ctrl + Shift + O.
As you can see, there isn’t any bookmark tied to the selected pre-created Fedora tag (or any other):
I can recreate this too. Although it does seem that the tags actually do get deleted before the crash.
I know that the Firefox maintainer for Fedora does prefer these kinds of things to be filed in bugzilla, so that’s probably the best approach here. (Even if it’s something wrong with the fedora-bookmarks package, Firefox shouldn’t crash!)
I installed Fedora 35 from scratch on another machine and I was able to mass-remove (Ctrl + Shift + O to access the ‘library’) all bookmarks and tags, no crashing either.
Since the I’ve installed software from the Python package index and some by compiling from the source (more or less blindly following instructions, some keyboard mapping software required sudo), I’ve decided not to report a bug at the time being.
I’ll reinstall Fedora and report back if the bug ever reappears.
The tags disappeared when imported (the bookmark backup/export includes any created tags) to a new Firefox profile. The issue may have been specific to my (potentially in some fashion borked) profile and I don’t know if there was enough data for a bug report.