Do you use browser extensions?

I love browser tweaks. Maybe it's a guy thing, always tinkering with some new gadget - although my inner obsessive-compulsive is secretly grateful that all of my new toys don't take up any physical space (I wonder how much of my stuff I could store "in the cloud"?) - but the joy that browser extensions give me knows no bounds.

Right now I'm particularly fond of the "Beautify Facebook" app, because it limits page-scrolling to posts only AND it filters out all of those annoying sidebar ads. I'd forgotten how much I couldn't stand those things until I made the mistake of changing my relationship status to "single", at which point I was overwhelmed by online dating service ads on EVERY page I visited (and thank you so much Facebook for insinuating that I need online help to manage that offline aspect of my life.)

What I'd really like to discover is whether or not anyone ELSE I know is using browser extensions, and if so, which ones? At some point I seem to have turned into a netgeek without realizing it - I'm really, really curious to hear what people have to say on the subject.