Definitely go get the Firefox Splash extension. I just installed it and it is simply amazing. It ads a loading screen to Firefox, which normally takes forever to load on my intel mac, but after I added the extension Firefox booted almost instantaneously. I'm not sure if it's the loading window that makes it seem like Firefox is booting faster, but either way it seems faster to me and I'll take it.
(It works with most Mozilla products including: Thunderbird, Firefox, and Sunbird)