The MCU is limited to only the apps provided by Tesla.
The browser has limited functionality (doesn't always work with Tesla's own website) - and the browser has no integration with any of the other apps (media player, navigation, calendar).
You may be able to access websites in the browser, but those sites will not have any access to the car's systems or the other apps running on the MCU.
With the new navigation software, Tesla has indicated they plan to provide Waze-like features, though that doesn't appear to be true with the current software.