Firefox Only - Access event object in rowExpandedStateChanged

[PunamSmahale]

gridApi.expandable.on.rowExpandedStateChanged($scope,function(row){
let event = event.target;

    //DO something based on which event fired - Expand single row or Expand all event

});

In Firefox, I cannot access the event.target, event is undefined here. I cannot change the signature of the above function inorder to pass event as an argument. That fails too.

In Chrome, it works.

Anyone encountered this kind ?