Since jQuery 1.6b, outerWidth gives a different result in IE8 vs FF4 if performing it on a <select> element that has padding and/or border.

http://jsfiddle.net/ZZz2d/ (compare it in FF4 and IE8)

Firefox 4 returns the css 'width' value (i.e. the "inner"). This is also what IE8 did prior to 1.6b. It is also the correct way, because select elements are just rendered that way (with the border-box model).

Internet Explorer 8 however now returns the width plus the padding and border (i.e. the "outer"). That may be what you expect from outerWidth, but it is not the actual visual width, which is what we're probably using the function for.