Firefox 25 just came out and.. you know.. loads of awesome tool bars if you want them. You can fill your whole screen!
I had the same issue. To fix, I launched IE 11 in Metro mode (or whatever the win 8 or 8.1 default desktop is called these days) then clicked on the wrench icon (page tools) on the bottom right black toolbar, and selected "view in the desktop". This now launches IE 11 with the missing menu bar and taskbars, assuming IE 10 or 11 were previously customized to show these in the first place. This setting held when rebooting as long as IE was launched from the regular desktop mode.