Profile backup does not work for me.

Hmmm, I've tried that once and it worked. Perhaps the Browser Console ( Ctrl+Shift+Alt+I ) could say more about this error. Try creating a backup locally on your Desktop.

Thanks for your note. I tried creating the backup on my local drive, and that seems to work. So either the problem was related to OneDrive, or whatever was causing the issue has fixed itself since yesterday.

I notice that it makes backups quite frequently. Whenever I start Firefox, it makes a fresh one, and then again after a few minutes if I'm using Firefox. If I just have Firefox open without touching it, no new backups are made. I assume it is snapshotting the profile as it changes. Is that normal? The documentation suggests it only creates a backup once per day (but the document here says every 60 minutes... my experience is that it seems to be tied to active use).

BTW, Ctrl+Shift+Alt+I didn't bring up anything for me. Is that only something in the development version of Firefox?

This is a follow-up on my own message.

I discovered the same problem again when I tried to put the backup on my D: drive (a secondary HDD). So the original problem wasn't due to the target being OneDrive; it was due to the target being something other than the local C: drive. Note that my OneDrive folder is mapped to my C: drive, but of course it is cloud-backed, which I'm sure makes it look different.

Since the behavior appears to be that Firefox creates a new backup every few minutes when I'm actively using it, I feel funny about frequently writing and rewriting a 100 MB file to my SSD. Perhaps it's not an issue, but my preference would be to use my HDD... only that doesn't work.