I'm trying in Firebug a code decripted in theJavascript definitive guide

PHP Code:
// Initialize the counter property of the function object.
// Function declarations are hoisted so we really can
// do this assignment before the function declaration.
uniqueInteger.counter 0;
// This function returns a different integer each time it is called.
// It uses a property of itself to remember the next value to be returned.
function uniqueInteger() {
return 
uniqueInteger.counter++; // Increment and return counter property

But when i execute it, firebug throws me reference error at uniqueInteger.counter = 0;

Why? It's a syntax allowed in some browser and not in other?