The Flashblock add-on makes Firefox worth using over everything else. Sure, I have to click one extra time to get a Youtube video to start, but it also keeps the 95% of Flash that is utter crap from ever running.
Lets you toggle colors (I HATE sites with dark backgrounds and grey text!), images, Flash, and Java off and on with a check box for each, right up top in the menu bar for instant access.
I am so used to browsing sites like FR in "plain text only" mode that when I login from an IE-using computer I sometimes don't recognize where I am....