User Agent: Mozilla/5.0 (Windows NT 6.1; rv:10.0) Gecko/20100101 Firefox/10.0 Build ID: 20120111092507 Steps to reproduce: Enter a web site (e.g. http://fiddle.jshell.net/AlienWebguy/CV3UA/1/show/ (the "test" block), 9gag.com) with elements that change their position correspondingly to the scroll position: In cases where they would normally become hidden under the browser's Navigation Toolbar, their position property is set to fixed to keep them visible. Expected results: This is done by JavaScript, but it could have been a lot easier with something like position:-moz-fixed-in-parent; Elements with this style will always "try" to stay in their parent node AND in the screen by changing their position, but if they can't they'll prefer to stay in the parent.

So, exactly like sticky positioning :)