Button elements (button, input[type=button], input[type=submit] all have a hard coded extra 1px 3px 1px 3px padding. This was done to mimic Firefox which has this hard coded, unremovable padding. IE does not have this so I think we are better off either just removing this hack. Mozilla bug: https://bugzilla.mozilla.org/show_bug.cgi?id=140562
Created attachment 43546 [details] Test case
*** This bug has been marked as a duplicate of bug 35629 ***