It's obvious (especially when loading large pages that take a while to load) that Adblock is actually still downloading the ads and displaying them before removing the elements. This should not be the case. Not only does this take the time/bandwidth to download the content that shouldn't be displayed, but that also shows up as false ad displays on metrics. Adblock should download the page source and filter any elements before downloading image files for ads. Noticed on Android 6, Firefox 48, Adblock 2.7.3.