I've found that when I chose a badge to track with "Select your next badge" is hard to use because I can't drag and drop the dialog. My taskbar hides the descriptions of several of the badges, so it's hard to know what the badge requirements are.
I'm not sure whether making it drag-able is good or not but the real problem here is that it doesn't gracefully accommodate short window heights. It seems to be positioned absolutely relative to the top of the page and doesn't scroll to reveal the bottom if it's off the page. This is something we should certainly address.
The dialogue should make an effort to be completely visible on the page - so should recognize short windows and adjust the vertical alignment. Alternately (or additionally), if the dialogue is taller than the window, scrolling down outside the dialogue's own scroll area should show the obscured part at the bottom.