Starting with firefox-63 , the sqlite database files in user profiles are open in exclusive mode to prevent collisions or concurrency issues of other programs trying to use them at the same time. Some gnome-shell extensions such as gnomenu , do this. This manifests itself as a regression when starting firefox after one such app has accessed the sqlite database file, with an error bar stating something to the effect of: "The bookmarks and history system will not be functional because one of Firefox's files is in use by another application. Some security software can cause this problem." Mozilla team is not going to change this functionality back to its previous behaviour, as exclusive sqlite database access in user profiles is a good idea. However, end-users can set the boolean pref 'storage.multiProcessAccess.enabled' to 'true' in about:config in order to allow concurrent access themselves. For more information, see https://blog.nightly.mozilla.org/2018/07/17/these-weeks-in-firefox-issue-41/#h.7x8cn7kvt374 and https://bugzilla.mozilla.org/show_bug.cgi?id=1472722
Nothing left to do for us.
