We are currently using an older JS minimization tool called JAWR. When minimizing Operative, it makes Firefox very angry with this:

...
        var loadedMethodName = '__operativeIFrameLoaded' + ++_loadedMethodNameI;
...

Firefox appears to treat that as a somewhat unknown operator, the triple-plus. This fixes it, obviously:

        var loadedMethodName = '__operativeIFrameLoaded' + (++_loadedMethodNameI);

Let me know if you'd like a pull request.