gistfile1.js

// Opening window/tab helper library for Mozilla
var $window = {
	open_in_new_tab: function(url){
		getBrowser().selectedTab = getBrowser().addTab(url);
	},

	open_in_same_tab: function(url){
		top.content.document.location = url;
	},

	open_as_popup: function(url){
		var mypopup = window.open(url,'popuppage','toolbar=0,scrollbars=1,location=0,statusbar=0,menubar=0,resizable=1,width=700,height=400,left=30,top=30');
		mypopup.focus();
	},

	focus: function(obj){
		obj.focus();
	},

	click : function(aEvent,url){
		if (aEvent.button == 2){
			this.open_as_popup(url);
		}
		else if ((aEvent.ctrlKey) || (aEvent.button == 1) || (aEvent.metaKey)){
			this.open_in_new_tab(url);
		} 
		else {
			this.open_in_same_tab(url);
			this.focus(window._content);
			
		}
	}
}

Usage:

<toolbarbutton id="myid" label="my button"  class="toolbarbutton-1" onclick="$window.click(event,'http://localhost/');" />