Some weeks ago I have written a little Addon for Firefox which lets you hide the toolbars for domains. This was mainly aimed at App-Tabs introduced in Firefox 4. The Addon was working for me and some friends but sadly the people on Firefox’s Addonsite obviously couldn’t get it to work and so it wasn’t hostet on there.
Today I have read a wikipage which stated that the Firefox developers are working on a similar functionality for a future release of Firefox. I think that’s great because this feature is really usefull.