Are both computers the same system?

Warning ! ! Only Copy the files you are told. We will avoid anything that might cause problems. Here is the list of files;

cookies: cookies.sqlite Do not bother. Cookies will be created when you return to the website. However, you will have to log in everywhere. And you may lose any settings that websites store on your computer.

extensions(add-ons, themes): it would be better to download them fresh. If you need to remember what add-ons you had, open the extensions sub-folder and look at the .xpi files

logins.json and key3.db [v58+]key4.db : These are the password files. Copy Both !

persdict.dat : custom dictionary - words you added to the dictionary

mimeTypes.rdf [v55+]handlers.json : What to do with what type of file.

places.sqlite : History and Bookmarks.

prefs.js : Your settings. Note: If you were having problems, this could be contaminated.

cert8.db [v58+]cert9.db and possibly cert_override.txt : Stores all your security certificate settings and any SSL certificates you have imported into Firefox. If removed, the cert8.db, cert9.db file will be replaced.

search.json.mozlz4 : file stores the user-installed search engines that are available in the Firefox v47+

search.sqlite file and searchplugins folder store the search engines that are available in the Firefox Search bar before Firefox v47

Copy these files from the old to the new. You may get a message that the files already exist. Choose to over-write for each file.

Hi Fred, I really appreciate your time and answering so promptly. The old "profile folder" was no longer in an active program, it was in a folder on a external drive. So there was no way to access the files that your described. However, the problem is solved, I'll explain what I did and hope it is clear.

I opened the location in Mozilla for the new Firefox folder, this is what I found; folders -Crash Reports, Pending Pings, and Profiles, files- installs.ini and profiles.ini. There was a similar folder in the now "non-active" folder on the external drive. I renamed all folders and files in the destination folder with a prefix of "x-". I then copied all of the mentioned folders and files from the external drive into the new Firefox folder. Closed the main Mozilla folder, clicked on the desktop icon of Firefox and it opened with the bookmarks, history, and passwords from before. I realize this is a bit unorthodox but it worked. Again thank you for your time. Sincerely, Robert

That was very good work. Well Done. Please flag your last post as Solved Problem as this can help others with similar problems. Go to that post and click the 'Solved' button to its right.