Ad filtering or ad blocking is removing or altering advertising content in a webpage. Advertising can exist in a variety of forms including pictures, animations, embedded audio and video, text, or pop-up windows. Very often it employs autoplay of audio and video. It is a known problem with most web browsers, including Firefox, that restoring sessions often plays multiple embedded ads at once. All browsers offer some solution to the problem, either by targeting technologies (Flash/Shockwave, Window Media files, etc.) that are used to deliver ads, targeting URLs that are the source of ads, or targeting behaviour characteristic of ads (such as the use of HTML5 autoplay of both audio and video).
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