ReferenceError: event is not defined error in Firefox

I've made a page for a client and I initially was working in Chrome and forgot to check if it was working in Firefox. Now, I have a big problem because the whole page is based upon a script that doesn't work in Firefox.

It's based on all "links" that have a rel that leads to hiding and showing the right page. I don't understand why this isn't working in Firefox.

For instance pages have the id #menuPage, #aboutPage and so on. All links have this code:

<a class="menuOption" rel='#homePage' href="#">Velkommen</a> 

It's working perfectly in Chrome and Safari.

Here is the code:

$(document).ready(function(){

//Main Navigation

	
$('.menuOption').click(function(){

  event.preventDefault();
  var categories = $(this).attr('rel');
  $('.pages').hide();
  $(categories).fadeIn();


});

// HIDES and showes the right starting menu
	$('.all').hide();
	$('.pizza').show();
	

// Hides and shows using rel tags in the buttons 	
	$('.menyCat').click(function(event){
		event.preventDefault();
		var categori = $(this).attr('rel');
		$('.all').hide();
		$(categori).fadeIn();
		$('html,body').scrollTo(0, categori);
	
	});
	

});	

You're declaring (some of) your event handlers incorrectly:

$('.menuOption').click(function( event ){ // <---- "event" parameter here

    event.preventDefault();
    var categories = $(this).attr('rel');
    $('.pages').hide();
    $(categories).fadeIn();


});

You need "event" to be a parameter to the handlers. WebKit follows IE's old behavior of using a global symbol for "event", but Firefox doesn't. When you're using jQuery, that library normalizes the behavior and ensures that your event handlers are passed the event parameter.

edit — to clarify: you have to provide some parameter name; using event makes it clear what you intend, but you can call it e or cupcake or anything else.

Note also that the reason you probably should use the parameter passed in from jQuery instead of the "native" one (in Chrome and IE and Safari) is that that one (the parameter) is a jQuery wrapper around the native event object. The wrapper is what normalizes the event behavior across browsers. If you use the global version, you don't get that.

It is because you forgot to pass in event into the click function:

$('.menuOption').on('click', function (e) { // <-- the "e" for event

    e.preventDefault(); // now it'll work

    var categories = $(this).attr('rel');
    $('.pages').hide();
    $(categories).fadeIn();
});

On a side note, e is more commonly used as opposed to the word event since Event is a global variable in most browsers.