It's really nice! The only thing is that I'm very lazy placing parentheses (especially for long equations). So 3+9)/4 for example instead of (3+9)/4 it would be nice if that would also work!
There's probably something I don't see, but I can't find how to actually use this extension. I'm typing simple math in the address bar (ex: "2+2") and I only see google results. What am I missing?