Ever since the major upgrade to 128, I noticed during backing up my system
that firefox-esr leaves all or almost all of the sqlite files open on exit
as if it crashed, leaving -shm/-wal files around by the hundreds.

I verified that it did so for things like…
PROFILE/storage/default/https+++www.kleinanzeigen.de/idb/3619119340leogcaarlof.sqlite
… when I didn’t even visit the site since the last time I can know it had
no -shm/-wal files lying around: I’ve added…

find ~/.mozilla/firefox/ \( -name \*-shm -o -name \*-wal \) -print0 | \
    while IFS= read -d '' -r name; do
        [[ -e $name ]] || continue
        sqlite3 "${name%-@(shm|wal)}" VACUUM
done

… to my pre-backup runs to get rid of these files, but the resulting
.sqlite files still differ between backup runs *due to* the VACUUM
(it’s noticeably more amount than before the major upgrade).

Additionally, this seems like it could lead to data loss, if it has
not finalised writing things before exit(2)ing the process by leaving
open databasish files.