Are you possibly using permanent Private Browsing mode (Always use Private Browsing mode; Never Remember History) ?

• https://support.mozilla.org/en-US/kb/private-browsing-use-firefox-without-history
• https://support.mozilla.org/en-US/kb/common-myths-about-private-browsing

Thanks for the reply; FF is set to standard protection and I do not use private browsing mode.

You can check for issues with (local) storage.

• https://firefox-storage-test.glitch.me/

Thanks for the link. LocalStorage - good. Totally working. QuotaManager - bad. Totally broken. IndexedDB - bad. Totally broken. Cache API - bad. Totally broken.

So, how do I fix these (if they are the problem)?

Firefox indicated that it was using 1GB for cookie and data storage. I cleaned everything out, twice. Logged in to Lastpass; Firefox reported using 5MB. Closed Firefox. Opened Firefox. I was logged out of Lastpass.

That result means that something is wrong with local storage that is also used by extensions to store their data.

You didn't use a profile used by the current release with an older Firefox version (i.e. downgraded the profile) as that can cause such issues ?

You can try to rename the storage folder in the profile folder to storageOLD to see if that has effect.

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

See also:

• /questions/1282610 Cannot access Gmail since update Firefox 74

Success! Renaming the storage folder did the trick. Reinstalled YouTube Video and Audio Downloader, logged in to Lastpass and have been testing for a couple of days, Everything works like it should. THANK YOU, cor-el !!