Cannot navigate between windows on Mac

As reported by Ulrich:

The training windows are much smaller than the Jisho window. When I have the Jisho window in front, the training window might be covered and there is no convenient way to activate them. I had to use for example Exposé to see all open windows and click the one I wanted. Perhaps you haven an idea, how to solve this. For example, the menu items of the "Train"-menu could not only open a window, but also activate an open window and bring it to the foreground. Perhaps a window menu might help too, where one can see, which windows are open and with which one can activate hidden windows.