I viewed the background image found out that it has something to do with Facebook. Still have no clue what it is.
I inspected the elements of the page I get this: <div id="AjaxProgress" class="xenOverlay" style="display: block; top: 0px; left: 0px; position: fixed; opacity: 0.540225;"<div class="content"><span class="close"></span></div>
This part of the HTML is highlighted and and flashing in sequence with the box in the top right corner: display: block; top: 0px; left: 0px; position: fixed; opacity: 0.540225
It is the refresh box. It is part of the auto-save for example if I type this text and then back out of the thread, my text will be saved in the text editor. To my knowledge there is nothing you can do about it.