Upgraded from what version? And was is x86 or x64 the old version?

Sorry to hear about this problem. If you haven't already, you may want to do a normal system shutdown and startup to release any file locks and complete any pending updates.

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

(1) A Refresh started 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.

It's a lot of things to check, but if you go step by step, it's not too bad.

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

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?

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

By the way, this article describes how to re-enable the Bookmarks Toolbar so you can double-check whether any of your bookmarks actually survived, or whether you have a "factory fresh" configuration:

Bookmarks Toolbar - Display your favorite websites at the top of the Firefox window

Upgraded from what version? And was is x86 or x64 the old version? I have no idea.

Did Firefox perform a Refresh? No Old Firefox Data on Desktop.

Does the Profile Manager list your immediately previous profile folder? Lists 3 folders; Default, Root and Local

Did Firefox orphan your old profile folder? I have a promising looking folder.

we can discuss next steps to recover use of them.

joeweir said

Did Firefox orphan your old profile folder?
I have a promising looking folder.

Great news. Okay, so, Firefox clearly has lost sight of that folder, or you would see it listed on the about:profiles page.

One technique to trigger Firefox to search for available profile folders is to hide its current list. Let's give that a try.

Return to your current Firefox settings (AKA Firefox profile) folder using either

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

In the first table on the page, on the Profile Folder row, click the "Open Folder" button. This should launch a new window listing various files and folders in Windows Explorer.

Leaving that window open, switch back to Firefox and Exit, either:

• "3-bar" menu button > Exit
• (menu bar) File > Exit

Once Firefox is closed, in Windows Explorer, you want to move "up" to levels. So you want to be viewing the contents of the Firefox folder, which should be

• folder name Profiles
• file named Profiles.ini
  To show all file extensions for confirmation, see: https://www.bleepingcomputer.com/tutorials/how-to-show-file-extensions-in-windows/
• possibly a folder named Crash Reports
• possibly other folders

The crucial file is Profiles.ini. That's the file which currently has an incomplete list.

Right-click Profiles.ini and Rename it to ProfilesOLD.ini and then click away to have Windows save the edit. When you start Firefox, it should display a profile chooser listing all of the profiles you saw in the Profiles folder. Can you get into the old one?