Hi,

I believe these are two different issues. The first one, with the folder name encoding, is a known bug and should be purely visual. The second one (which prevents the backups from being created) is the one we actually need to investigate here.

Could you please go to about:config, search for browser.backup.backup-debug-info and share its value? (For reference, see Configuration Editor for Firefox.)

Also, after trying to create a backup, could you please check the Browser Console for errors? (You should be able to open it with Ctrl+Shift+J, but please see the linked article for more details.)

Here is value from about:config: {"lastBackupAttempt":1777916372,"errorCode":{"name":"BackupError","stack":"#prepareStagingFolder@resource:///modules/backup/BackupService.sys.mjs:1976:25\n","unremovableContents":["C:\\Users\\***\\AppData\\Roaming\\Mozilla\\Firefox\\Profiles\\zg0lv6vz.default\\backups\\snapshots\\2026-03-12T22-12-27Z.zip","C:\\Users\\***\\AppData\\Roaming\\Mozilla\\Firefox\\Profiles\\zg0lv6vz.default\\backups\\snapshots\\archive.html","C:\\Users\\***\\AppData\\Roaming\\Mozilla\\Firefox\\Profiles\\zg0lv6vz.default\\backups\\snapshots\\staging-0","C:\\Users\\***\\AppData\\Roaming\\Mozilla\\Firefox\\Profiles\\zg0lv6vz.default\\backups\\snapshots\\staging-1","C:\\Users\\***\\AppData\\Roaming\\Mozilla\\Firefox\\Profiles\\zg0lv6vz.default\\backups\\snapshots\\staging-2","C:\\Users\\***\\AppData\\Roaming\\Mozilla\\Firefox\\Profiles\\zg0lv6vz.default\\backups\\snapshots\\staging-3"]},"lastRunStep":5}

Thank you! I believe this issue should get resolved with the next Firefox major update (see bug 2029240). Let me check with the team, though.

Meanwhile, as a temporary workaround, you can either manually delete all the files in the snapshots folder (just copy the path from the Browser Console error message), or delete the backups folder entirely (the same path as before, but one folder higher). The second one should work better, from what I understand.

See also /questions/1577922 where the OP had an exact same issue (and where I stole the recommendations from :D)

Looking forward to your update on whether the above workaround(s) help!

(The encoding issue is now tracked under bug 2036892, but as I said, it's purely cosmetic.)

Thanks - removing "Firefox backup" did not help (it was empty anyway, I removed old backups before). However, removing all files from \snapshots folder helped. Backup created automatically. I noticed that after backup, snapshots folder gets empty. So issue was that firefox was unable to remove files from it ?

I think they should add info to their support article to suggest users emptying this folder too, instead of only removing target backup folder.

So issue was that firefox was unable to remove files from it?

Yes. I hope that the patch in bug 2029240 will prevent such kind of errors from happening, and there will be no need in manual action. But we'll see :D

It looks like they pushed fix for this bug early: https://www.firefox.com/en-US/firefox/150.0.2/releasenotes/ It was targeted for firefox 152.

Yep, it's been uplifted. Hope it will resolve the issue, but if you encounter this (or any other) bug in the future, please reach out!