I customize the hell out of Firefox. So much that I’m thinking of buying an USB memory stick just so that I can use my profile everywhere, i.e. for using Portable Firefox.
First of all there is the bookmarks toolbar hack, as far as I know I’m the only one who does this:
I’ve removed a few menus items, and placed the Bookmarks toolbar items on the menu-bar itself. No need to use a separate toolbar, this saves a lot of screen space.
Extensions I can’t live without are:
SmoothWheel makes reading huge web-pages fun, and easy on the eyes.
Super DragAndGo is another huge continence. You highlight words, and just drag & drop them somewhere on the screen to search on Google. Or drag & drop links to open in new tabs.
The usual which I have talked about before, a lot: Web Developer, All-in-One Gestures, Adbock, Live HTTP Headers and Greasemonkey of course.
If there is only one thing you’re going to install, install Greasemonkey, and then head over to greasemonkeyed.com and pick up scripts for your favourite sites. And don’t forget to check out Mark Pilgrim’s greasemonkey scripts.
I’ve tinkered around with the profile for so long that I can’t really remember all that I’ve done. I just take periodic backups just so that I don’t ever have to start from scratch. Actually I’ve cleaned it up quite a bit recently, removed a few extensions and scripts that I didn’t use.
If you have problems with Firefox being too slow or something, the fault almost surely lies in your profile. Here are some instructions to start with.