Unless you have backups someplace . . . . .

When a computer loses power without shutting down, files can be corrupted.

Perform a System File Check to fix corrupted system files

Win 7, 8, 10, Vista: https://support.microsoft.com/en-us/kb/929833 Win XP: https://answers.microsoft.com/en-us/windows/forum/all/windows-xp-scan-and-fix-disk-errors/6fe2827a-4be6-4bc1-8083-5139b5aa3a3d

Wiki - Windows 10 System File Check http://answers.microsoft.com/en-us/windows/wiki/windows_10-update/system-file-check-sfc-scan-and-repair-system-files/bc609315-da1f-4775-812c-695b60477a93

After the above, Use Microsoft ScanDisk {web link}

FredMcD said

Unless you have backups someplace . . . . . When a computer loses power without shutting down, files can be corrupted. Perform a System File Check to fix corrupted system files Win 7, 8, 10, Vista: https://support.microsoft.com/en-us/kb/929833 Win XP: https://answers.microsoft.com/en-us/windows/forum/all/windows-xp-scan-and-fix-disk-errors/6fe2827a-4be6-4bc1-8083-5139b5aa3a3d Wiki - Windows 10 System File Check http://answers.microsoft.com/en-us/windows/wiki/windows_10-update/system-file-check-sfc-scan-and-repair-system-files/bc609315-da1f-4775-812c-695b60477a93

This is not relevant to what I asked.

I have my own backups for some addons but they are quite old.

I gave you those links so that you can make sure your system does not have any other problems.

Back up and restore information in Firefox profiles.{web link} I use an add-on that makes backups of my user profile, Just In Case. Unfortunately, it is not compatible with the current Firefox.

Every now and then, open the profile folder and create a copy of the current profile as is to another location on your hard drive. This way you will have a backup.

If you do this each day, you will not lose much data. This should be done with Firefox Closed.

Note: In case you need to restore from these backups, you may need to overwrite old or corrupted files.

So Firefox does not keep backups of anything? Anything goes wrong and your data is gone completely?

I know I can do manual profile backups, but if I had them I wouldn't be here

The only backups Firefox makes are the bookmarks.

I assume you already restarted Windows again in case some file locks need to be released.

It's strange to find Firefox settings were reset without your extensions being removed -- it sounds like only half a refresh, which doesn't make sense.

Can the extensions store new data (e.g., new userscripts) normally?

Were you already on Firefox 66 at the time of the crash? Firefox 66 migrated extension settings from JSON files (renamed to storage.js.migrated) to SQLite databases (via IndexedDB). It's possible that the crash with Firefox running corrupted some of those databases.

I don't know of a repair tool for corrupted extension data databases. There is an arduous looking method to re-migrate your Firefox 65 extension data described in this blog:

https://blog.mozilla.org/addons/2018/08/03/new-backend-for-storage-local-api/

Those might be newer than your last backup.

Alright, I'll try the described method.

I wondered why in the extension settings were .migrated files that Firefox didn't seem to be loading the data from.

So previously settings were in "browser-extension-data", where are they now? "storage/default"?

jscher2000 said

Can the extensions store new data (e.g., new userscripts) normally?

Yes, seems so

Shajirr said

I wondered why in the extension settings were .migrated files that Firefox didn't seem to be loading the data from.

The .migrated extension is added to storage.js after the migration so it doesn't get migrated again.

So previously settings were in "browser-extension-data", where are they now? "storage/default"?

I think that's right.

jscher2000 said

I don't know of a repair tool for corrupted extension data databases. There is an arduous looking method to re-migrate your Firefox 65 extension data described in this blog: https://blog.mozilla.org/addons/2018/08/03/new-backend-for-storage-local-api/ Those might be newer than your last backup.

This process worked! Loaded back all my data for uBlock and Tampermonkey, which were the most important ones!

Thanks for posting this link!

Process is actually much simpler than it looks - basically you go to addon settings folder, copy .migrated file and remove .migrated from its name, uninstall the addon you need to restore the setting for, close browser, reopen browser then reinstall addon - that's it.