Re: WTF is "tiles"?
You may find the most visited tiles useless but I find them very useful. You can also pin them in place on the new tab. When I open a new tab they provide links to six important sites I have pinned (El Reg and a bunch of sys admin stuff mostly) and three frequently visited sites. Very handy indeed.
Fortunately they will continue to do so since I am not a new user and any new install of Firefox is quickly synced with my others.