One of the terrific built-in features of Firefox 4.0 is the ability to create app tabs for your favorite websites. The only downside is the extra steps required to do so by going through the Context Menu. With the Easy App Tabs extension you can reduce the work to a simple and quick double-click.
Another nice bonus with this helpful extension is that you will not need to restart Firefox after installing it! Just add the extension to Firefox and start double-clicking away on those tabs.
Note: The extension currently works with Firefox versions 4.0b4 – 4.0.*.
Easy App Tabs [Mozilla Add-ons]