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http://dev.w3.org/csswg/cssom-view/#terminology [[ Elements and viewports have an associated scrolling box if it overflows its content area and either has a scrolling mechanism or the used value of the 'overflow-x' or 'overflow-y' property is 'hidden'. [CSSBOX] ]] It appears that overflow:scroll should have a scrolling box always. Change to: Elements and viewports have an associated scrolling box if it has a scrolling mechanism or it overflows its content area and the used value of the 'overflow-x' or 'overflow-y' property is 'hidden'. [CSSBOX] This affects the behavior of document.body.scrollTop in quirks mode when body has overflow:scroll but no overflowing content. See bug 23603
https://dvcs.w3.org/hg/csswg/rev/456fdd8be0d5