I think I have quite a lot of them (Firebug, greasemonkey, NoScript, Scarpbook, etc.) but the thing is, I don't close my browser every hour or so. Startup times are nothing if you don't do startups too often.
What would bother is any performance impacts with them running. However we don't have figures for that.
What would bother is any performance impacts with them running. However we don't have figures for that.