Is it possible to identify certain add-ons in firefox even if they aren't in the user agent string, or is that the only information you get from the client? Wo

Is it possible to identify certain add-ons in firefox even if they aren't in the user agent string, or is that the only information you get from the client? Would be cool if it could tell that I use pentadactyl, stylish, ad-block plus etc. etc.