* adapt to Log4Moz -> Log renaming (FF 27+)
* fix typo (Cu.reportError)
show/hide mechanism in place: clicking on tray icon or closing a window.

NOTE: a WndProc on each mozilla window is not needed for this.
don't cache and update windows[wid].visible, windowsCount, visibleWindowsCount

Because the number of windows will generally be small, this is not worth the
effort.