As I wrote before, there are plans in motion to require Private Browsing mode compatibility in Firefox extensions. In order to make the lives of our reviewers easier, we need a tool to help them review extensions for Private Browsing compatibility.
I've laid out the specifics of such a tool in a wiki page. The plan is detailed, with a lot of links to documentation which would help you do the specific tasks needed for building this tool. If you've ever wanted to get started building an extension, or were waiting for an exciting extension idea which would help Mozilla folks do their job better, this is a very good opportunity.
I'll be available to help you through the details of building this tool. Don't hesitate, jump in!