Do you prevent default action in keyboard and click handlers? In Opera and Firefox I can sometimes see focus outline and text selection flashing, probably activated by my 1-key keyboard shortcuts.

Good question. I looked at the code and it appears we preventDefault for mouseup and mousedown but not for keyup and keydown. I will ask around why that's the case. Can you give me an example keyboard shortcut where this is happening ?

W and S in Opera select paragraphs (if you enable advanced shortcuts like I did). In Firefox I'm able to drag and select whole canvas (entire screen flashes light blue).