The weird update behaviour is because file got replaced while Firefox is running. On Windows and macOS the updates happen on next start (whenever you choose tha

The weird update behaviour is because file got replaced while Firefox is running. On Windows and macOS the updates happen on next start (whenever you choose that to be) so it's not an issue; on Linux updates are handled by your system package manager, so they couldn't line it up as nicely. Of course that also means you could end up having queued but not applied updates for a long time on Windows and macOS…