FF 79 beta2 (latest beta): (I'm using win7 x86)
FF 79 have new storage-sync-v2.sqlite, storage-sync-v2.sqlite-shm, storage-sync-v2.sqlite-wal files in profile folder. When I exit Firefox, storage-sync-v2.sqlite-shm, storage-sync-v2.sqlite-wal files are kept and not deleted unlike cookies.sqlite-wal, cookies.sqlite-shm, favicons.sqlite-shm, favicons.sqlite-wal. By the way, CCleaner > Custom Clean > Applications > Firefox > "Internet Cache" option deletes all *.sqlite-shm, *.sqlite-wal, so CCleaner deletes these two files too. storage-sync-v2.sqlite-wal store addon settings that uses the sync API, so I lose the addon settings changed that is not yet applyed to storage-sync-v2.sqlite. So, please don't delete *.sqlite-shm, *.sqlite-wal with that option. CCleaner > Custom Clean > Applications > Firefox > "Compact Databases" option deletes all *.sqlite-shm, *.sqlite-wal too(so, CCleaner don't have to deletes it in "Internet Cache" option), but apply these to *.sqlite files before delete it, so I don't lose my data.
I'm sorry for my bad english.
Regards.