I did expect the community to get interested in extending the Private Browsing mode by developing extensions, but I didn't expect it to happen this soon!  I'm happy to announce that the first Private Browsing extension has been developed by the community member Kurt Schultz! This extension adds a toolbar and a status bar button to Firefox for quick access to the Private Browsing feature, and lets you toggle a few of the underlying preferences as a bonus!  Grab it while it's hot from AMO!

Here's a screenshot provided by Kurt:

Toggle Private Browsing extension in action

Thanks for the great work, Kurt!