If you installed the latest Firefox 3.5, you’ll notice that it’s consistently slow at start-up taking at least 10-15 seconds. I have looked for some solutions but I think I only have found what we call a temporary fix. This issue has already been addressed by the Firefox team. As for myself, I have just reverted back to 3.11 both in Windows Vista and Ubuntu 9.04 Jaunty Jackalope. I don’t want any of the hassle.
If you want to sneak into the current discussion about this issue, have a look at this link.