TubeStop is an extension for Mozilla-based Web browsers that disables the autoplay on YouTube videos. This means that you can open multiple YouTube videos in tabs in the background without them all starting to play at once. TubeStop also disables the autoplay on YouTube videos embedded on non-YouTube.com sites (MySpace, for example).
If you like TubeStop, check out my other YouTube-specific Firefox extension: YouTube Comment Snob. It adds powerful filtering controls to YouTube comment threads.
If you're having trouble with the extension or would like to see a new feature added, e-mail me at firstname.lastname@example.org or leave a comment below.
Note: watch the TubeStop section of my blog for information on updates to this extension.