As the title says, the back and forward buttons only work when they would navigate to a different domain. This is essentially useless behavior because back and forward buttons are mostly used to navigate with one domain. This bug might have something to do with hiding everything except the domain in the address bar (which is clearly the fault of a designer who thinks their work is to make things pretty rather than useful, but I digress).
Also, the “Back button” option under Customize Controls binds to returning to the browser from within a 360 experience. This is not what “back” means in a web browser. Not sure what went wrong with these egregious UX errors because it’s otherwise a wonderful app.