Pressing the PS button while playing a PlayStation Vita game will bring up the system’s OS. You can access a number of features available in the Vita such as your music collection, friend list, and the system’s Twitter. When you’re done, you can hop right back into the game you were playing.
The sad thing is… you’re unable to access the web browser while playing. This, in other words mean that you will have to exit the game(yes, exit, not pause) if you want to access the system’s web browser.