The number of hooks in Firefox seems likely to be a contributing factor in it being somewhat slower (in some regards) than Chrome and Safari, which are both extremely basic in their customizability and extensibility via third party plugins. Flexibility does usually have a cost, in software and in physical systems, and Firefox definitely goes to the extreme on flexibility. I'm about 50/50 on whether the trade is worth it, and I waffle between Chrome and Firefox as my primary browser.<p>Firebug and AdBlock Plus are both quite demanding plugins, having to analyze and manipulate the DOM so often and in so many ways. I don't think one can expect them to have no impact on performance.