Good news from Mozilla, they have released the beta version of Prism - formerly webrunner. I have always thought of a browser like that, and I think I have tested webrunner before.
Using Prism you can directly run you favourite web application from your desktop. As Mozilla folks says "a distraction free browser", free from all the clutter that a browser has.
Currently I am doing some test on my Kubuntu laptop. Will post results as the test progress. You can also get the latest version from this link.