PithHelmet sounds like a good tool, but I go for a more global solution -- a proxy to filter all of my browser connections. Being a web developer, I tend to switch through browsers fairly often to test pages (mine or others') and surf, so a solution glued to one browser doesn't cut it.
Privoxy is my filter solution of choice, an actual proxy server that runs on OS X and is configurable through a web interface. Check it out if you've never considered it. It's easy to turn on and off via a bookmarklet toggle, and endlessly customizable. I've been using it for years now with no problems or complaints.