That's interesting. It looks like Mozilla balks at the syntax of something like:

var fn1 = function fn2() { … }

IE accepts this, but does not see fn1 as being equal to fn2 and therefore, any attempt to remove the listener by calling .detach('onclick', fn2) fails.

Both IE and Mozilla however, are happy with something like this:

var fn1, fn2;
fn1 = fn2 = function() { … }

In that case, fn1 and fn2 are equal to each other and the event listener removal should succeed.

What about IE behaviour when 1 function == 2 different objects (FunctionDeclaration in love with FunctionExpression) ?

var fn1 = function fn2() { alert('hey there!'); };
function att() { myDiv.attachEvent('onclick', fn1); }
function det() { myDiv.detachEvent('onclick', fn2); }

p.s. Wonderful blog!