absolute positioning display issues

Here's a distinction in rendering absolute position amongst browsers. How should a absolute positioning of bottom:0px; function?

I'm quite proud of my resizable background here .
It works very well – until the content gets too long and makes the page scroll. Then, on Safari, the position is set to the bottom of the browser window, while IE presents it as the bottom of the page, which seems correct to me. Mozilla doesn't even bother to display them, which is a better solution than doing it incorrectly, I think.

Thoughts?

Ian