Double-tap the Home button to access the app switcher -> Swipe left or right to find the browser -> Swipe up over it to close it.
*You can quit up to three applications at a time by placing you fingers over them and and swiping up.
Here is a video demo of how to close apps (and web browsers) through the app switcher:
If you don’t receive the email in the next 2 minutes please check your junk folder, and add [email protected] to your safe sender list.