Did you replace the files while Firefox was closed?

You can use the button on the "Help -> Troubleshooting Information" (about:support) page to go to the current Firefox profile folder or use the about:profiles page.

• Help -> Troubleshooting Information -> Profile Directory:
  Windows: Show Folder; Linux: Open Directory; Mac: Show in Finder
• http://kb.mozillazine.org/Profile_folder_-_Firefox

If there is a problem with logins.json then Firefox usually will add a .corrupted.

Did you check the permissions of the files if you copied them from another location?

Firefox uses two locations for the Firefox profile folder, so make sure to look in the correct location. Location used for the main profile that keeps your personal data in "AppData\Roaming".

• C:\Users\<user>\AppData\Roaming\Mozilla\Firefox\Profiles\<profile>\
• ~/Library/Application Support/Firefox/Profiles/<profile>/

Location used for the disk cache and other temporary files in "AppData\Local".

• C:\Users\<user>\AppData\Local\Mozilla\Firefox\Profiles\<profile>\
• ~/Library/Caches/Firefox/Profiles/

In the event that the passwords information is lost, you should record all information in a separate text file somewhere else on your hard drive, or written down. You can easily copy and paste if you need to do so. If you are concerned about someone else looking at that file, you can compress it using a password.

cor-el said

Did you replace the files while Firefox was closed?

Yes.

As for the permissions I can't see any problems either. SYSTEM, the username I'm logged in as, and administrators all have full control.

I didn't bring this up earlier as I assumed it wasn't relevant but the old profile is from macOS while the new installation is on windows 7. So the directories look like

C:\Users\[username]\AppData\Roaming\Mozilla\Firefox\Profiles\[profile folder] \Users\[username]\Library\Application Support\Firefox\Profiles\[profile folder]

Is the fact that it's between different OSes potentially an issue?

FredMcD said

In the event that the passwords information is lost, you should record all information in a separate text file somewhere else on your hard drive, or written down. You can easily copy and paste if you need to do so. If you are concerned about someone else looking at that file, you can compress it using a password.

I still have my old 56 profile that is still functioning on another OS. Thanks, but I'm fine. Only thing that's at stake here is the convenience.

ouyihkj said

Is the fact that it's between different OSes potentially an issue?

Different systems may store data differently.

... anyone?

https://support.mozilla.org/en-US/questions/1202039#answer-1070656

flofl0 said

https://support.mozilla.org/en-US/questions/1202039#answer-1070656

Edit: According to my understanding, I can facilitate a fallback from key4.db to key3.db by removing the newer SQLite versions. I'm not sure exactly what this consists of. Is simply deleting key4.db sufficient?

Yes, IF the original key3 file is still there.