Very simple extension, does exactly what it says and nothing more. If you don't believe me, audit the code yourself. My only complaint is the lack of a whitelist.

Compatible with Waterfox! This add-on has absolutely no options, no icons, nothing! It works completely automatic, selecting a random agent string for each domain visited by the user. Unfortunately, there is no way to select/edit available agent strings, whitelist/blacklist domains or anything at all.