It only wigs out after it times out. It works fine in Firefox for me. I did not understand exactly what it was doing at first, but it seems to be a trainer for precisely timing the space between your keystrokes.

It only does that for me if I hit the ' or / keys - all others work just fine. (FF on macOS 10.12).

Sorry about that! Have only tested it on Chrome and Arc so far. I initially got messed up myself by the Vimium extension but just had to disable that for the page. Will take a look at this, thanks.