root/lang/javascript/userchrome/LocationbarNewTab.uc.js

// open in New Tab from location bar
BrowserLoadURL = function(event,post){
        gBrowser.userTypedValue = content.window.document.URL;
        if((event && event.altKey) ||
           gURLBar.value.match(/^javascript:/) ||
           gBrowser.userTypedValue == 'about:blank'){
          loadURI(gURLBar.value,null,post,true);
        }else{
                _content.focus();
                gBrowser.loadOneTab(gURLBar.value,null,null,post,false,true);
        }
}