Mozilla Mouse Bug

Reported 1 November 2005 to Quirks Mode.

Text Input with Mouse Events Registered

Description

The above text input element has event listeners registered for both "mouseover" and "mouseout". One should see pairs of mouseover/mouseout events when the mouse enters/exits the text field (as one sees in IE 6). On Firefox 1.0.7, several strange things occur:

A normal mouseover is followed by a mouseout, even while the mouse is still over the text field.
When attempting to read the mouseout event.relatedTarget.nodeName property, an exception is thrown.
Another mouseover event is fired, this time with event.relatedTarget set to the same element as the element on which the event is registered.
The reverse sequence occurs when the mouse leaves the element.

Workaround

In order to respond to simply mouseover/mouseout events, one must perform both of the following:

Ignore all mouseover/mouseout events that have event.relatedTarget set to the same element as the element on which the event is registered.
Attempt to access event.relatedTarget.nodeName and, if an exception is thrown, ignore the event.

This workaround is compatible with IE 6, as that browser does not send the extraneous events in the first place. This workaround is forward compatible only if Mozilla fixes the extraneous event bug when it fixes the event.relatedTarget.nodeName access bug.