There is a bug with the line 210 at least in Firefox using a trackpad from a Macbook pro:

wheelSpeedDelta = -(evntObj.deltaY || evntObj.detail || (-1 / 3 * evntObj.wheelDelta)) / 40

When evntObj.deltaY is equals to 0, it goes to evntObj.detail which is also equals to 0, which goes to (-1 / 3 * evntObj.wheelDelta) returning a NaN.

Also only the deltaY is used even if the axis is set to x.

Here is a pull request that correct this issue:
#51