So how about this <!DOCTYPE html>
<html>
<head>
<style type="text/css">
.innocent-class {
background: url(http://www.google.com/images/logos/ps_logo2.png);
width: 240px;
height: 400px
}
.justForTesting, .advertise_ads {
width: 240px;
height: 400px;
background: #fff
}
</style>
</head>
<body>
<div class="innocent-class"> <!-- just don't call it "advertContainer" :) -->
<div class="advertise_ads justForTesting">
advert here!
</div>
</div>
</body>
</html>When Adblock Plus finds an element with a class (for example) .advertise_ads, it will hide that element. If it does, the "please don't block my ads!" background-image (in this case, the Google logo) from the parent element will be visible. If the advert isn't blocked, the advert will cover the replacement image. Try changing advertise_ads to something else such as sdpfjsdfjp, and the advert will be visible.