I don't think this util functions should be concerned with private browsing, neither they should ignore arguments that are private windows. I think that should happen at the next tire. More precisely only way danger is that high level APIs will by accident wrap private window, but that can only happen if the get a reference by enumerating wins, by getting an active win, or get a ref via observer notification, which in our case is more or less replaced by window tracker. IMO this module should not even know be concerned by private browsing, instead we should have a second tire module that just wraps `windows` from this module and ignores skips privates. It also should expose window tracker that skips privates and I don't know if `getMostRecentBrowserWindow` is even a concern, if it is then wrapped version of that too (although I find `null` return value awkward).