Mozilla also released Firefox 1.0.2 today. As with Thunderbird, there are security fixes, so upgrade now.
The folks behind TweakXP have developed Firetune version 0.5 for Firefox 1.x users. It changes the configuration of the Firefox browser to use the most common and popular optimization settings all wrapped up in one handy little executable. I noticed a bit of a boost. It's not huge, but every little bit counts.