If you're a Firefox user and you use several of the many useful extensions available for the browser, you've probably run into the thorny problem of one extension disabling or altering the functionality of another one. This can be quite annoying. For example, AdBlockPlus is extremely popular as an extension for blocking pop-up ads and banners, but (sometimes unintentionally) there are quite a few Firefox extensions that disrupt it, drawing regular complaints from people trying new extensions, or upgrading existing ones. Mozilla is now proposing a set of policies to police this problem, prompted by a recent catfight between extension developers. The proposed policy changes raise questions about just how much freedom extension developers should enjoy.