Mazila extension. How to clear the address bar?

Question

Mozilla Firefox

Good afternoon. I want to write a replacement for a new bookmark. Wrote this:
browser.tabs.onActivated.addListener(function(){
browser.tabs.query({'active': true, 'lastFocusedWindow': true},function(ta){
var tab = ta[0].url ;
if(tab=='about:newtab'){
browser.tabs.update({'active': true, url:"index.html"});
}
})})
But the page opens and the address bar contains the path to index.shtml. Is there a way to clear the address bar so that everything works like it does in other browsers.