This is pretty cool: Mozilla Firebird: Tips & Tricks
I especially liked making this change:
Speed up page rendering
By default, Mozilla Firebird doesn't try to render a web page for 250 milliseconds, because it's waiting for data. If you add the code below to your user.js file, Mozilla Firebird immediately tries to render the page, even without complete data. The drawback is on slower machines where doing a "reflow" may actually cause the total page load time to be longer.
Do a search on the page and you'll find it. The "Force frames to be resizable" feature is cool, too. Haven't had to use it yet, esp. since frames seem to be falling out of favor lately (as they should).
You can also block ads, but it makes some pages look weird.