To work in Chromium, Chrome, Iron a simple click on the script link should be enough. For newer versions of Chrome the script must be saved and dragged & dropped in the extensions page or you can use the Tampermonkey extension.
To work in Epiphany it is required to install the Greasemonkey extension from Epiphany extensions.
To work in Midori it is required to enable the User Addons extension.
To work in OmniWeb it is required to install GreaseKit add-on. If the add-on doesn't work it must be enabled for OmniWeb from Safari.
To work in QupZilla a simple click on the script link should be enough.
To work in Internet Explorer it is required to install IE7Pro add-on. The script must be saved as ViewTube.ieuser.js in the user scripts directory of the IE7Pro add-on and enabled from its properties dialog window.
On Linux and *BSD platforms the video plugins that can be used are Mplayerplug-in, Gecko-mediaplayer, Totem, VLC, Kaffeine, Dragonplayer, Kmplayer.
On Mac platform the video plugins that can be used are Quicktime and VLC.
On Windows platform the video plugins that can be used are Windows Media Player, Quicktime and VLC.