The creator of Tubestop, a Firefox extension that stops autoplayback of Youtube videos, noticed that his extension did also prevent the advertisement from appearing which he attributes to the fact that Youtube ads are only displayed on the main site and not when the videos are embedded or syndicated.

Tubestop therefor stops the ads in Youtube effectively and should be downloaded by everyone who does not like to see this kind of ads on Youtube.

Update: TubeStop is still available on the Mozilla Add-ons repository. The extension is a restartless add-on, which means that you do not have to restart the web browser to complete the installation. It works right away on all new tabs that you open, and after a reload on old tabs as well.

When you open a web page with an embedded YouTube video, which can be on the primary YouTube website or a third party site, you will notice that the extension stops the video from playing right away. It will stop videos or video ads that are played before the actual video. The following screen is then displayed in the video’s location.

You can click anywhere in the video frame to play that video right away.

Firefox users can download and install the latest version of TubeStop directly from the Mozilla Add-ons repository.