Comment 6 for bug 769169

As far as I can tell from the description, this bug isn't actually specific to tiled windows. It applies to any situation where there are multiple windows open for the same application, and it's hard to tell which one is showing its menus in the menu bar. Tiling two windows is just the worst case of this, because then window overlapping is not available as a visual cue as to which window is focused.

The lack of distinction between focused and unfocused windows is bug 534799, so I'm marking this as a duplicate.