That is a methodology. But it has evolved into something a bit easier with the FF feature known as "sync".

Step 1: On the old pc, sign in/log in to the FireFox Account using a simple/favorite email address.

Step 2: Initiate the "syncing", which will upload your user data to the account. After syncning ends, sign out of the FF account.

Step 3: On the new pc, sign into the FF account with that email address you had previously used. Then initiate the syncing.

Step 4: Sign out of the FF account.

Sometimes the syncing takes several minutes. So you can monitor whether or not it is syncing, go into the FF options and to the sync section. There will be a button "Sync Now" . If its not present, then FF is syncing. If it shows up, you can press it to see if Syncing is all done.

I am very happy for your help. Thank you very much!

You can copy certain files with Firefox closed to the current profile folder to transfer or recover personal data. Note that best is to avoid copying a full profile folder.

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

• bookmarks and history: places.sqlite
• favicons: favicons.sqlite
• bookmark backups: compressed .jsonlz4 JSON backups in the bookmarkbackups folder
• cookies.sqlite for the Cookies
• formhistory.sqlite for saved autocomplete Form Data
• logins.json (encrypted logins;32+) and key4.db (decryption key;58+) for Passwords saved in the Password Manager
  key3.db support ended in 73+; to use key3.db in 58-72, make sure to remove key4.db
• cert9.db (58+) for (intermediate) certificates stored in the Certificate Manager
• persdict.dat for words added to the spell checker dictionary
• permissions.sqlite for Permissions and possibly content-prefs.sqlite for other website specific data (Site Preferences)
• sessionstore.jsonlz4 for open tabs and pinned tabs (see also the sessionstore-backups folder)