Flashblock is an extension for Flock, K-Meleon, Mozilla Application Suite, Mozilla Firefox, Netscape Communicator, Netscape 8, and SeaMonkey that prevents Macromedia Flash "movies" from automatically playing when a web page is first loaded. Flashblock is primarily used to prevent banner ads that play audio or video from starting, but also to reduce load time of banner-filled pages. It is also one of the few effective ways to block Oddcast SitePal animations from appearing.
Flash movies can still be played in these browsers with Flashblock enabled, but must either be explicitly started by clicking on the movie, or adding the website the movie is loaded from to Flashblock's whitelist.
Flashblock version 1.5.6 is compatible with Firefox 1.5 to 3.0.x, Netscape 9 and Flock.
Flashblock version 1.3.9 is compatible with most other Mozilla based browsers including older versions of Firefox.
Identically-named browser extensions have now been written for Internet Explorer and Opera.