For those of you who like to do things manually, PCTipsBox explains how you can “double the speed of Firefox”, in their article.How to Double Firefox Speed

The article goes into some detail, and there are a couple of suggestions I didn’t know, including the values content.interrupt.parsing, and content.max.tokenizing.time.

Of course, you can use the FasterFox plugin for Firefox to do much of this automatically! But plugins do tend to slow things down a little on startup!