Why variable hoisting after return works on some browsers, and some not?

Question

alert(myVar1);
return false;
var myVar1;

Above code throws error in IE, FF and Opera stating that return statement has to come in the function. But

Answer 1

It is JavaScript Hoisting thing, Simply in other words, we are trying print the value of the variable , which is not holding any value

Javascript will render the above code as:-

var myVar1
alert (myVar1)
return false

To clarify more i refered the link javascript hoisting: http://www.ufthelp.com/2014/11/JavaScript-Hoisting.html