"We want to reduce the overall risk [to Firefox] by evaluating where there are unused features, and then getting rid of that old code... We want Firefox to have a tighter code base," she told Techworld. Snyder founded security consultancy @stake before joining Microsoft, where she was involved in signing off the code for Windows XP SP2 and Windows Server 2003, before leaving to found Matasano Security. She joined Mozilla last week.
Inevitably, the older a program becomes and the more revisions it goes under, the more code that is unused or unneeded will be lying around. Cutting the fat, even if it's something that no one would normally pay attention to, is usually a good idea.