Descargamos el plugin, abrimos un terminal y tecleamos
wget http://github.com/pilt/spotify/tarball/master
tar zxf pilt-spotify-b3069c7cfa4002990da623135d5ff4b454d67e00.tar.gz
cd pilt-spotify-b3069c7cfa4002990da623135d5ff4b454d67e00
sudo apt-get install libx11-dev libglib2.0-dev libpurple-dev build-essential
make
make install