Firefox stuck trying to install helper tool.

If I update Firefox from my admin account, I have no problem. But sometimes, in the user account, Firefox wants to update. If I update from there, putting in the admin user name and password, it tries to install a "helper tool" and gets stuck. Then every time I try to launch Firefox from the user account, it tries to install the helper tool and refuses to launch. Here is the answer to my own question: Delete User Name/Library/Caches/Mozilla folder. Restart into the admin account and update Firefox. Now all will be well.