Until recently, document.body.mask() [and document.body.spin()] correctly blocked the content [e.g. buttons not clickable until unmask() / unspin() happens] of document.body with IE, Firefox and Chrome.
This still works with Firefox and Chrome, but no longer with IE11 (11.0.9600.16476)!
Example: http://jsfiddle.net/Uh42Q/1/