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 > "?" Help > 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, and any session history files they contain.

Did Firefox perform a Refresh? - no "Old Firefox Data" folder

Does it list immediately previous profile folder? about:profiles lists: "Default Profile yes" "Root Directory C:\Users\Admin\AppData\Roaming\Mozilla\Firefox\Profiles\ka9ybb5p.default" "Local Directory C:\Users\Admin\AppData\Local\Mozilla\Firefox\Profiles\ka9ybb5p.default"

Orphan old profile folder? - lists 08b00r3z modified today 8.10 and ka9ybb5p modified 9.41 today (ie. now)

Xelador said

Orphan old profile folder? - lists 08b00r3z modified today 8.10 and ka9ybb5p modified 9.41 today (ie. now)

Do you want to try using the other folder? What you can do is:

(1) Exit Firefox

(2) In the Firefox folder, that's one level up from the Profiles folder, right-click Profiles.ini and rename to ProfilesOLD.ini (or similar).

When you start Firefox, it should regenerate Profiles.ini based on what is found in the Profiles folder, and offer you a choice of which profile to use.

Does that get you back into the old one?

Afraid Firefox just created a new .ini file - no choice offered

If you go to the about:profiles page, is the other profile you mentioned listed there now? Hopefully you can switch there.

Nope: "Default Profile yes" "Root Directory C:\Users\Admin\AppData\Roaming\Mozilla\Firefox\Profiles\84jg5j5f.default" "Local Directory C:\Users\Admin\AppData\Local\Mozilla\Firefox\Profiles\84jg5j5f.default"

The other folder that shows in Windows explorer (08b00r3z.default) is not shown in about:profiles

Okay, I don't know what went wrong there. You may have to edit the Profiles.ini file by hand in that case. The change would be find:

84jg5j5f

and change it to

08b00r3z

(while Firefox is closed).

Profiles.ini is a plain text file, so when saving changes, make sure it doesn't switch to Rich Text or any other format Firefox won't understand.

Note that you can also use "Choose Folder" in the Profile Manager to register a 'lost' profile.

• http://kb.mozillazine.org/Profile_Manager
• https://support.mozilla.org/en-US/kb/profile-manager-create-and-remove-firefox-profiles

Editing profile.ini worked. Back to normal. Thanks.

Trying to open ProfileManager in Windows 10 just opens starts firefox.