YouTube automatically keeps a history of all the videos you’ve watched recently. Not a problem usually, but there are times you may not want your boss for instance to see what you’ve watched recently, or maybe if you are using a shared computer.
You can clear your history manually, but there is a way to clear your YouTube history automatically if you’re a Firefox user. The YouTube History Bleach extension will automatically clears your YouTube history every time you view a video.#
Yet another reason to switch to Firefox if you haven’t already done so.
More: YouTube History Bleach