Actually FF is slow because of all the addons...which incidentally(and unsurprisingly) cause many memory leaks.
Even without the add-ons, Firefox is slower in start up times as opposed to IE, Chrome, Safari etc.
Nevertheless, Firefox was a life savior. At the time, only Safari and IE were the alternative options and IE was pretty much hated. Safari on the Windows platform again, buggy and prone to crashes for the most part.
