I have FF3 and with or without the preloader, my Vaio still takes what seems like forever(OK slight exaggeration but it aint swift) to load, and no I don't have myriad FF extensions added on. To be fair, most things take forever to load, but I came across this thread and switched browsers to try something different. This was the same before I installed Norton 2008 so its not the security software slowing it down. I've run every security test that's out there to try and find a bug that may be slowing this thing down, but everything comes up clean. Going to two gig of Sony RAM seemed to make the performance worse, so I went back to one gig and drinking Fosters.
I now just shrug my shoulders and wave my hands in acceptance in a very "Ce la vie" Gallic fashion, which frankly, has me more concerned than my Vaio's performance.