i hated Firefox for a long time, simply because of its start-up time. well, not strictly true, i couldn't see the point of it when Maxthon loaded quick and had loads of options built in.
but, eventually (not until Firefox 3.5) i saw the light. i still hate how long Firefox takes to load - so much so, i make it autostart after my machine has booted, and then i use ActualWindowManager to prevent me from closing Firefox prematurely, i.e. i get a dialog popup asking if i really want to close FF when i click the "X". this makes me think twice about whether i really want to close it - sometimes i do, most of the time i don't, i just click on it by habit.
so, FF automatically opens at the beginning of the day and stays open all day. doing it this way makes it feel like the fastest browser there is - obviously because i never see it loading.
i really have way too many FF extensions to contemplate using any other browser. which also means i probably won't be using FF4 for a long time, let alone FF5. not unless the extension developers are quick to update their stuff.