Hi Pircsi2007, sorry to hear about this problem.

Did you already try shutting down and restarting Windows in case there is a file lock that needs to be removed or maybe a permission problem?

If Firefox is really not able to find your profile folder, you may first need to create a new one. Three steps:

(1) Edit your Firefox shortcut temporarily to call up the profile manager

This is how it works on Windows 7, hopefully it's similar on Windows 10):

• Desktop shortcut: right-click the icon, choose Properties
• Pinned taskbar icon: right-click the icon, right-click Mozilla Firefox, choose Properties

Windows normally will select the Shortcut tab. If not, go ahead and click the Shortcut tab.

You'll see the Target highlighted. On Windows, that usually is no more and no less than one of the following (depending on 32-bit/64-bit):

"C:\Program Files (x86)\Mozilla Firefox\firefox.exe"
"C:\Program Files\Mozilla Firefox\firefox.exe"

After that, add one space and then -P (that's a hyphen or minus character, then the letter P).

Click OK to save the change.

(2) Create a new profile

When you use the edited shortcut, Firefox should display a Profile Manager listing all the profiles it is aware of and having an option to create a new one.

Don't delete anything here!

Click the Create Profile button, assign a name like Oct2018, and skip the option to relocate the profile folder. After creating the profile, select it and start Firefox in that profile.

Firefox in the new profile should just look brand new. Otherwise, We'll look into restoring data in the next reply.

Does Firefox run without crashing?

If you have a Firefox Account set up for the Sync service, you could use that to try to restore settings. Otherwise, see the next reply for further suggestions.

(3) Undo shortcut change

Follow the steps under #1, but this time, delete the -P from the end of the Target path.

If you can't bring back all your data using Sync, here are some additional places to look for a lost profile folder.

(A) Desktop: "Old Firefox Data"

If a Firefox Refresh ran, your old data would be in a folder on your desktop named "Old Firefox Data". Do you see a folder like that? Does it have recently modified files inside?

(B) Firefox data folder

I recommend tweaking two Windows settings first:

(i) Set Windows to show hidden files and folders

https://support.microsoft.com/en-us/help/14201/windows-show-hidden-files

(ii) Set Windows to show all file extensions

https://www.bleepingcomputer.com/tutorials/how-to-show-file-extensions-in-windows/

Then explore to the Firefox data folder. You can use this shortcut in the Windows 10 search box, or explore the full path:

• Shortcut: %APPDATA%\Mozilla\Firefox
• Full path: C:\Users\your-user-name\AppData\Roaming\Mozilla\Firefox

In this folder you should find the following (possibly more):

(1) Folder named Profiles

(2) File named Profiles.ini

Double-click into the Profiles folder to see what folders you have there. One should be the fresh one you created following the steps in the first reply. Do you see other folders here? Do they have recently modified files inside?

If you found recent data files, then we can discuss how best to get those into your new profile (or how best to lead Firefox to use your old profile).