The browser object might help. The lock/unlock orientation actions are mentioned in the manual.
Lock the display of the game to a portrait or landscape mode only, if the current platform supports this. This only has effect on mobile devices. The game may have to already be displaying in fullscreen (using the Request fullscreen action) before the orientation can be locked. Unlocking the orientation restores whatever behavior was set before locking, such as automatically changing orientation depending on the way the device is being held.