Immanuel, hope this article helps. https://support.mozilla.org/en-US/kb/back-and-restore-information-firefox-profiles

If it does not, then another possible avenue is to create a new profile then restore only specific individual files from the backup to the new profile. See the following article for a list of the individual files that you may wish to copy into the new profile folder (with Firefox closed, naturally): https://support.mozilla.org/en-US/kb/about-your-important-data-and-their-files

I did what the first article describes and it simply does not work. I think it has to be on the same device, otherwise something breaks. Mozilla should update the article.

The second approach where I copy just a few files works, but not completely. the passwords are transferred, but when I go to a site it does not know the password is available and I have to enter the login and password manually. Still, it works.

Immanuel, I believe that some things such as add-ons might rely on absolute hard drive paths.

And so some users may experience issues when they copy the contents from one folder to another on a different computer, if the new profile path does not match the original path exactly?

You possibly might be able to fix the results of the first link's method by re-installing any add-ons. Or by first creating a new profile with a custom path that matches the original profile path exactly, and then replacing its contents with a copy of the backup folder's contents?

But if you are done tinkering with profile restoration, then you might be able to restore the password autofill functionality in the new profile.

If you go to Tools menu / Settings and search for "Fill usernames and passwords automatically" is it checked?

Also, if you right-click in a login field for a known site, then you may see a manual option for filling in the sign in info, if this doesn't happen automatically. Or you can left-click inside the edit box and see if an option to fill the fields in appears in a drop down menu. (although if you are using a Primary Password then this may need to be entered before these options appear)