setInterval() and setTimeout() don't fit all use cases. Additionally the last few releases of Firefox have sped up the interval to almost 50% the defined value e.g. `setTimeout('foo,5000);` will execute in 2500ms This provides a firefox shunt as well as allowing for the interval's delay to be adjusted, paused, and restarted

complexInterval.js

function complexInterval = function( fn , t ) {
	var	_delay = t? parseInt(t) : 0
		
	,	callback = fn
	
		//stores the time of last callback execution for play/pause behavior and firefox shunt
	,	lastExecution = (new Date()).getTime()
		
		//shunt for firefox, which executes setTimeout up to 50% early
	,	checkExecution = function(){ var time = (new Date()).getTime() - lastExecution; if (time >= _delay) return true; timeout = setTimeout( (function(){ once(); }), time ); }
		
		//execute the callback and setup the next one
	,	once	=	function(){ if( checkExecution() ){ callback(); lastExecution = (new Date()).getTime(); timeout = setTimeout( (function(){ once(); }), _delay );}}
		
		//initiate the callback loop
	,	timeout = setTimeout( (function(){ once(); }) , _delay )
			
	,	timeElapsed = 0
	;
		
	Object.defineProperty( this , 'delay' , {
			get	:	function() { return _delay; }
		,	set	:	function(b) { _delay = parseInt(v); }
	});
	
	this.reset = function(){
		if( timeout !== false ) {
			clearTimeout(timeout);
			timeout = false; //sometimes unless I explicitly set it to false it doesn't clear.
			timeout = setTimeout( (function(){ once(); }) , _delay );
		}
	};
	
	this.pause = function(){
		if( timeout !== false ) {
			clearTimeout( timeout );
			timeout = false;
			timeElapsed = (new Date()).getTime() - lastExecution;
			}
	};
							
	this.play = function(){
		
		//reset lastExecution so it's not far in the past
		lastExecution = (new Date()).getTime() - Math.max(0, _delay - timeElapsed);
		
		timeout = setTimeout( (function(){ once(); }) , Math.max(0, _delay - timeElapsed) );
	};
							
}