Many people complain that the Mozilla Firefox take up a lot of time during start up. To speed up firefox start up time you can try to install Firefox Preloader.
Firefox Preloader is a free utility that is designed to speed up firefox start up. By loading parts of Mozilla Firefox into memory before it is used it improve the speed of the startup time.
It uses about 14MB of your system RAM, but if you have at least 1GB of memory installed you won't notice this small loss.
I've tried this software personally, it's really able to speed up the firefox start up time. You might wan to give it a try
http://sourceforge.net/projects/ffpreloader/
