Does not work well with multiple windows

[rasendubi]

Problem: I have multiple Chrome windows open with different tabs. The extension does not work well in that setup.

Steps to reproduce:

1. Open two windows
2. Open http://xxx in the first window
3. Open http://yyy in the second window
4. Move mouse from window two to window one
5. Open extension

Result:
Popup is shown for http://yyy, but should be shown for http://xxx