A disabled button should not receive and should not fire onclick mouse events.

Steps to reproduce: click the disabled button below.

Disabled button

Expected results: nothing should happen after clicking the disabled button.

Reference: disabled: When set for a form control, this boolean attribute disables the control for user input. (...) it cannot receive user input
coming from HTML 4.01, section 17.12.1 Disabled controls

This bug has been reported at connect's IE beta feedback as bug 333934.