SMTube is not a plugin for your browser but...
SMTube is an application that allows to browse, search and play YouTube
videos. Videos are played back with a media player (by default SMPlayer)
instead of a flash player, this allows better performance, particularly with
HD content.
You will need to install the latest version though (the one in the Trisquel
repo does not work). You can download the .deb from the website but I highly
recommend you compile it from source (it's easy). The latest source is here
->
http://sourceforge.net/projects/smtube/files/SMTube/15.5/smtube-15.5.17.tar.bz2
