Public Fox is a great FF extension that allows you to take control over you entire FF environment when it is in use by others. Public Fox allows you to lock downloads, so no one can download anything while you are away, lock add-ons, so that no one can tamper with your extensions (mainly this one that is preventing them from doing anything fun), lock the FF options, the “about:config” page and the addition/removal/options of bookmarks, to prevent completely messing up your browser. There is also a filter for the file extensions that you do not want downloaded (.exe, .avi …). In order for you to use any of the locked features, all you have to do is enter the password that you set in the Public Fox options. The only thing that you can really do with this extension activated is to remove all of the search engines that reside in the search bar in the top right-hand corner.
There is a bit of a bug, however. If you try to install a new extension while FF is locked down, it seems that it is not installed if you do not know the password. But, after a restart of FF, you will see that it is, in fact, installed. You just cannot configure the extension outside of its default settings. But this extension is still a great one for anyone from an average FF user to even public libraries or schools.