http://jsfiddle.net/b85D4/5/

In Firefox the selected value is 1. In Chrome the selected value is 2.

removeAttr has special handing for boolean attributes to set the corresponding DOM property to false: https://github.com/jquery/jquery/blob/master/src/attributes/attr.js#L86

Removing an attribute and setting the DOM property to false are very different. In this case, as specified (http://www.whatwg.org/specs/web-apps/current-work/multipage/the-button-element.html#dom-option-selected), setting the property to false means setting the dirtiness to true. This changes how the option should react to "selected" attribute changes. In the test case, it means that adding the "selected" attribute at the end should not select the option.

Firefox respects the specified behaviour and does not select the second option.