The chance of finding a music video is very high on Youtube. It does not really matter if you are looking for the latest Billboard charts videos or videos from the Seventies, they are all available on Youtube. One thing that is missing though are lyrics for those music videos. While some uploaders add the lyrics in the description most do not add them.
Youtube Lyrics changes that. It’s a Greasemonkey script that adds a lyric element to each Youtube video. A container Lyrics will be displayed beneath the Video description and will show the lyrics of that music video if expanded. The title of the video should at least contain the song title of the song.
A drop down menu provides access to different lyrics
databases on the Internet and you can try to find the lyrics in the other databases if the default one does not reveal any results.

You need the Firefox
Greasemonkey extension and the
Userscript that adds the Lyrics to Youtube. [found at
GOS]
Lyrics for Youtube Videos