Copy the ViewTubeHandler Applescript application to your HD.

In Firefox/TenFourFox:
- type about:config
- create a new boolean preference network.protocol-handler.expose.viewtube and set it to false
- open the “First launch” html page and click the link
- when asked, point Firefox to ViewTubeHandler
Viewtube should now be able to open videos in QuickTime Player.