In the Control Panel, find Google Toobar for Firefox. Click twice and allow its removal. Restart Firefox.

First off you should disable it on the Addon option so that will allow you if need be to uninstall it. Sometimes you have to disable it before you can uninstall it.

I very much appreciate the hint, but I said the add-on had been disabled already in an old upgrade of Firefox, but there was no place to uninstall. I solve it by going to the Control Panel and uninstalling Google Toolbar for Firefox. That got rid of it. Finally I failed to mark this a solved, and I'm sorry for that. I am looking for a place to mark this solved, but do not see that. If the administrator or someone in charge can do that or tell me how, I'll be pleased.