I've just got all the plug-ins sorted for Firebird and thought AI'd have a go at tweaking it.
I use IE6 at work every day and it's not bad, but FiREBIRD is definitley quicker. Especially if you put this code in your user.js file where the number is the time in ms that Firebird waits before page rendering. you could set it at 0.
user_pref("nglayout.initialpaint.delay", 50);
THis works fine on broadband and now pages seem to load pretty much intentaeously. It's going to be pain going back to IE in the morning!
http://texturizer.net/firebird/tips.html has got the details