Firefox Search Engine Box - Adding etc..

[PoorDoggie]

Hi,

I have this code on my website to "install" a new search engine into the Firefox search engine box:

function addEngine(name,ext,cat,type){
	  if((typeof window.sidebar == "object") && (typeof window.sidebar.addSearchEngine == "function")){
		window.sidebar.addSearchEngine(
		  "http://mycroft.mozdev.org/external.php/" + name + ".src",
		  "http://mycroft.mozdev.org/external.php/" + name + "."+ ext, name, cat );
		}
        else{
		  alert("You will need a Mozilla based browser to install a search plugin.");
		}
	}

you can see it here: http://6yd.net with a firefox browser...

I need to know:
1. How to make it the default search engine in that person's firefox browser...
2. How to figure out if they already have my search engine on their list...

Thanks
Tom