Here are a few Firefox plug-ins that we will be lucky to never see put into production.
Replaces all youtube videos with Rick Rolls.
Converts all images on a web page to random pictures of cats with amusing captions.
Automatically replaces any scientific content with fundamentalist interpretations.
Converts all names and headlines to Tarantino movie characters, and inserts random lines from Tarantino scripts.
Converts any professionally designed web page into a Myspace abomination.