Allow users to have either 16:9 or 4:3 aspect ratio for tabs when in landscape rotation.
Option to go full screen. Smartphone displays are not wide enough so a full-screen mode will help a lot when using device in landscape rotation.
Zoom capability. I know users can zoom in websites now also. But this zooming that I am suggesting is different. In this zooming elements of web page increase in size while still fitting inside the screen (just like on desktop browsers).