Go to the Mozilla Add-ons Web Page {web Link} (There’s a lot of good stuff here) and search for what you want.

Thanks for the suggestion FredMcD, but unfortunately I haven't found a solution in the Add-Ons.

Peter said

A somewhat older friend of mine keeps opening firefox multiple times. Often over 40 sessions are running, slowing the PC down to almost zero response. Is there a way to prevent this?

So why are you letting them do this? Are they using the limited account? You can place restrictions on what it can do. If they are doing this they aren't a friend. They should get their own computer before they do damage to yours.