The best protection is your own protection. What I mean by that is don't install add-ons unless you are certain it is safe. Add-ons don't just get installed out of the blue. They get installed from downloading programs (make sure you check any options) as often they are checked for you. BrowserProtect
is a good Firefox add-on.
You're better of looking at this
section yourself and reading the reviews. I don't see why a developer would need
to create an add-on for what you're asking as add-ons don't get installed by themselves, some human intervention would need to take place i.e. installing a program and clicking next without reading what it says.