Stop on lost focus

[TheCandyman]

I have a jquery script that correctly rotates several images in a loop after showing each for a few seconds. I'm noticing in the newest Firefox and Chrome browsers, and found the same after searching, that it I move off the tab or minimize the browser that the JavaScript stops/pauses until focus is returned.

I see the wisdom in pausing JS when it's not being viewed to save wasted CPU and battery power so i need to tweak this script to only run on focus. It does work correctly in IE9. I have tried a few different things(ex. window.onblur = ) but can't get thing to work correctly so I'm in need of help. Here is my code:

$(document).ready(function() {

	//Set Default State of each portfolio piece
	$(".ImageRotaterPaging").show();
	$(".ImageRotaterPaging a:first").addClass("active");
		
	//Get size of images, how many there are, then determin the size of the image reel.
	var imageWidth = $(".ImageRotaterWindow").width();
	var imageSum = $(".ImageRotaterReel img").size();
	var imageReelWidth = imageWidth * imageSum;
	
	//Adjust the image reel to its new size
	$(".ImageRotaterReel").css({'width' : imageReelWidth});
	
	//Paging + Slider Function
	rotate = function(){	
		var triggerID = $active.attr("rel") - 1; //Get number of times to slide
		var image_reelPosition = triggerID * imageWidth; //Determines the distance the image reel needs to slide

		$(".ImageRotaterPaging a").removeClass('active'); //Remove all active class
		$active.addClass('active'); //Add active class (the $active is declared in the rotateSwitch function)
		
		//Slider Animation
		$(".ImageRotaterReel").animate({ 
			left: -image_reelPosition
		}, 500 );
		
	}; 
	
	//Rotation + Timing Event
	rotateSwitch = function(){		
		play = setInterval(function(){ //Set timer - this will repeat itself every 3 seconds
			$active = $('.ImageRotaterPaging a.active').next();
			if ( $active.length === 0) { //If paging reaches the end...
				$active = $('.ImageRotaterPaging a:first'); //go back to first
			}
			rotate(); //Trigger the paging and slider function
		}, 5000); //Timer speed in milliseconds (3 seconds)
	};
	
	rotateSwitch(); //Run function on launch
	
	//On Hover
	$(".ImageRotaterReel a").hover(function() {
		clearInterval(play); //Stop the rotation
	}, function() {
		rotateSwitch(); //Resume rotation
	});	
	
	//On Click
	$(".ImageRotaterPaging a").click(function() {	
		$active = $(this); //Activate the clicked paging
		//Reset Timer
		clearInterval(play); //Stop the rotation
		rotate(); //Trigger rotation immediately
		rotateSwitch(); // Resume rotation
		return false; //Prevent browser jump to link anchor
	});	
	
});