A really cool and helpful extension. I have one complaint, though:
Right after I got it to work correctly, I noticed that the initialize function returns one extra mouse than I actually have. For example, the first thing I tried is using my actual mouse and my mouse pad for my laptop. Both devices worked, but the number of mice was 3, not 2. The 0 mouse in the array wasn't an actual mouse.
Later I tried it with two mice, and my mouse pad. Same thing happened, except this time number 2 was non-functional.