80f1c82 worked everywhere except IE9: http://swarm.jquery.org/result/2255930

Investigation traced the root cause to a mishandling by that browser of box-sizing: content-box, particularly in combination with overflow: scroll... specifically, getComputedStyle seems to always report content box dimensions, even for border-box elements, and the lack of accounting for scrollbars means that round-trip set operations shrink such elements: https://jsbin.com/zotomuqoho/edit?html,css,js,output