I only want to block adverts when they are intrusive and I feel bad about blocking acceptable ads. Most ad blockers will allow you to whitelist a website but I often will not notice that the ads are being blocked and thus not white list it. What I want is an ad block extension to Firefox that only turns on for new sites when I tell it to, although it should be able to remember which sites I want it on for. I can't think of the best way to explain this which is why I couldn't find a solution on the web.

Does anyone know of an adblocker with this feature and how do I turn it on?