One of Request_Denied cause is you use geocoder (placemark defined by text address), or tries to use search feature.
And you didn't have Google Maps API Key (or not configured).
Today Google requires API key, and it add more billing cases. Read it terms.
If you will break its limits (and not have billing, ie not pay) - you'll get overlay image "For developer purposes" over the map and some of features will not work (geocoding, streetview feature (not in case pegman on map) etc)
When they add this terms, I started development for OSM. Now when I have free time I still adding features to OSM extension, but it is still not completely implemented ajax loading map objects (placemarks and paths), but it is in my plans. As for documentation
As for tabs - it is not third party library (as in google), but I just write my own tab feature It is more flexible and I can add what I want