Firefox makes backups of your settings. Just search your system for files with the extension .json. You should be able to use that file to import your bookmarks. I think it will also contain your history and home page but I am not 100% as I have mine turned off.

I recommend you back up your json file from time to time.

I'm sorry to hear about your data loss. Firefox shouldn't lose settings in the middle of a session just from logging out of a website and logging back in. Possibly Firefox had the problem from the time you started it but it wasn't immediately apparent??

If you haven't already, before doing any file moves/deletes/reinstalls, you may want to do a normal system shutdown and startup to release any file locks and complete any pending updates. One user reported it took three shutdown/restarts to sort out his issues.

If your data does not magically reappear, the most likely scenarios for complete data loss are:

(1) A Refresh occurred but the migration of data from your old profile to your new profile was incomplete, or
(2) Your old profile was locked, so Firefox ignored it and created a new one

Here's how to investigate those two possibilities:

Did Firefox perform a Refresh?

Unless it was interrupted in progress, you should find a folder on your desktop named Old Firefox Data. Inside would be a semi-randomly-named folder with freshly updated files. Do you see anything like that?

If so, we'll suggest how to rescue key files or completely restore the earlier profile folder.

If not...

Does the Profile Manager list your immediately previous profile folder?

To check on that, inside Firefox, type or paste about:profiles in the address bar and press Enter/Return to load it.

This page should list all the profiles Firefox is currently aware of. If you see a profile that is not currently set as default that looks promising, scroll down to it and click the Set as default profile button below that profile, then scroll back up and click the Restart normally button. (There are some other buttons, but I think those are still "under construction" so please ignore them.)

Firefox should exit and then start up using the other profile. Is that the right one?

If it's not there...

Did Firefox orphan your old profile folder?

Here's how to check whether there are additional profile folders in the standard location in addition to the one you're using. Start by opening your current Firefox profile folder using either:

* "3-bar" menu button > "?" button > Troubleshooting Information
* (menu bar) Help > Troubleshooting Information
* type or paste about:support in the address bar and press Enter/Return

In the first table on the page, click:

* Windows: the "Open Folder" button, to launch a new window listing various files and folders in Windows Explorer.
* Mac: the "Show in Finder" button, to launch a new window listing various files and folders in Finder.

In the Windows Explorer address bar, click the capitalized word Profiles to move up one level in the folder hierarchy. More than one folder here by any chance? Do the files in those folders look like they were last updated around the time of the update?

(Mac users: please do what you need to do in Finder to check up one level...)

If you've got any promising looking folders, we can discuss next steps to recover use of them.

Darvin said

Firefox makes backups of your settings. Just search your system for files with the extension .json. You should be able to use that file to import your bookmarks. I think it will also contain your history and home page but I am not 100% as I have mine turned off.

Hi Darvin, the only true backups are the bookmark backups, with the file extension .jsonlz4 (the lz4 was added when Firefox started compressing them). Since they are stored in the profile folder with the other settings, we need to help track down the profile folder.