Adblock Plus or an equivalent adblocker. They all go by the same name (adblock) but developed by different people. Some are better than others. The original/official is the one I linked for Firefox. But really, as long as it has the "adblock" name, it's pretty much a must have. I also have a scroblr extension for my browser, which detects youtube, google music, pandora, etc. I love my last.fm. I also have an app on my computer for scrobbling from itunes. I used to be real big on extensions, but since I've switched to safari I haven't really used many of them.
I suggest Adblock Edge. Adblock Edge is a fork of the Adblock Plus version 2.1.2 extension. The fork provides the same features as Adblock Plus 2.X and higher but without the "acceptable ads" feature. Adblock Edge was primarily branched off from Adblock Plus 2.1.2 source code package. (Firefox only.)