Server.UrlEncode - IE and Firefox?

I have a problem, my url is treated difrent in firefox and IE
 
Urlen.Append("&kategorie1="+Server.UrlEncode("Tøj & sko"));  
Firefox in urlen:
kategorie1=T%C3%B8j+&+sko
 
IE
kategorie1=T%c3%b8j+%26+sko
I you see firefox malin its wrong..what can ii do?

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