Very mysterious indeed. It works OK for me on Opera, IE, and Firefox. I do think the hit area is a bit left shifted but it still works OK for me. It sounds like an Html5 implementation problem in Firefox.

My suggestion is to try the CreateJS export library. You will have to re-export and use different .js files. I really would prefer not spending time fixing KoolMoves export library issues if the CreateJS library works well.

If the problem also occurs with CreateJS and I can create a most simple example, I can present it to the CreateJS support team.