> @Gozala, @erikvold Otherwise, we should just match what is done for other tabs API, what are we doing for require("sdk/tabs").activeTab?

In high level API for windows `activeWindow` will return last non-private active window. In low level API for windows (`window/utils`) `getMostRecentWindow` will return active window regardless of weather it's private or not.

As of this module I don't know which group should we put it, in fact I had it removed ~2 years ago when I just started with project, but then we had to put it back because some of the big new changes had lot's of tests relying on this.