I'm afraid I don't have any real solution, since I get Firefox from the play store, but its my secondary browser; I get Mull from Obtainium (kinda like a Librewolf for android), you might look into that? I know this is kind of not what you wanted to hear though and im sorry
Instead of trying to parse the old stuff, could you just run something like borg and then delete the old copypaste backup? Or are there other files there that you need to go through? I ask because I went through a similar thing switching my backups from rsync to borg
No problem! I'm glad it was helpful