AdBlock and Adblock Plus are two popular ad and pop-up blocking extensions that work in Firefox, Chrome and Safari Web browsers. Adblock and Adblock Plus block not only pop-up advertisements, but virtually all advertisements that appear on websites as well.
When a browser loads a page that contains a pop-up advertisement or a normal advertisement, the advertisement must load through a website URL. Ad blockers work by comparing URLs that are loading on a Web page with a list of URLs that are known to serve up advertisements. If the URL that is loading on a page is the same as one of these URLs in the list, then the ad blocker stops the URL from being loaded, and thus blocks the pop-up or other advertisement.