See Import login and password data from a file. This feature is available starting in Firefox version 80. You have 79.

Thanks for the reply, in fact I hadn't noticed the number of realise ... Would you know any tricks to be able to do it without downloading the beta version?

No, you have to wait a week to the release of 80.

I'm running version 84 and have the same problem. I'm trying to import my information from an old machine to a new one and find this very frustrating. If I'm running a version higher than 79 why doesn't it work?

I'm running version 84 and have the same problem.

Meaning, you can't see the entry Import from a File…? It means the feature is disabled. To enable it, go to the about:config page, find the signon.management.page.fileImport.enabled preference and toggle it to true.

You do have a CSV file from the old computer with your logins ?

If you do not yet have new passwords in 84 then you can copy logins.json and key4.db over to transfer the logins.

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 Folder/Directory:
  Windows: Open Folder; Linux: Open Directory; Mac: Show in Finder
• https://support.mozilla.org/en-US/kb/profiles-where-firefox-stores-user-data