TYPO3 Core

I use Typo3 4.2.8 when i log in the BE with IE6 and i try to work(open a page, edit content) i will become the js error message "Object is required (line 3788) (prototype.js)"

it should be this line:
return {
x: event.pageX || (event.clientX +
(document.documentElement.scrollLeft || document.body.scrollLeft)),
y: event.pageY || (event.clientY +
(document.documentElement.scrollTop || document.body.scrollTop))
};

i use the companion.js for javascript debuging.

(issue imported from #M11751)