Upgraded Ubuntu, Lost Years of Firefox Files [duplicate]

The Firefox snap app is the default web browser in Ubuntu 21.10. You can uninstall the snap version and install the .deb version with the command:

sudo apt install firefox && sudo snap remove firefox

The .deb version of Firefox should be able to see your profile.

I had the same issue. Here is what I did to quickly fix this issue.

1. Uninstall firefox snap with:

   sudo snap remove firefox
   

2. Install firefox snap with:

   sudo snap install firefox
   

3. Run snap with:

   snap run firefox
   

With the last command you should see the following lines in the terminal:

Importing existing firefox profiles from /home/xxxxxxx/.mozilla/firefox
Found default profile: xxxxxxxx.default
Import done in 1.826 s

After that all bookmarks and login/password should be back.