Here's some conifg settings you can change to help speed Firefox up, and fix a problem with it acting sluggish after being inactive for a while.
Type about
:config in the address bar and hit enter.
Scroll way down to network.http.pipelining, double click on it and set the value to "true".
Set network.http.proxy.pipelining to "true".
Set network.http.pipelining.maxrequests to 8.
Scroll down some more to nglayout.initialpaint.delay and set it to 0.
Now right click, click New -> Boolean and type config.trim_on_minimize for the preference name. Set it's value to false.
If you picked up
Firefox 0.9 and don't like the new theme, you can get the old theme from
http://www.quadrone.org/graphics/#Qute