This is but one function the original Siemens Webwasher and Proxomitron did years ago (Proxomitron released in 1999 was one of the most essential browsing apps ever created IMO). You could choose to rewrite ad links and replace them with a graphic of your choice. You could do *anything* - proxomitron was God-mode for browsing... This add-on seems pretty boring to me and I'd rather the ad space was removed (as Opera and Adblock do) than filled with more distractions.