Need Script For Floating Image At Lower Right Corner Of The Window

I'm looking for a cross-browser (IE, Netscape, Mozilla/FireFox, Opera, Safari) javascript that will keep an image (or <div>) in the lower right corner of the browser window whenever part of the web page has been scrolled vertically. I did find a script on the internet that was supposed to fit my needs, but I found it didn't work as advertised. (I included that script below.)

Requirements:
- I'm using "Frames" and the frame I want the image/div to appear in is the main content frame that sits against the right and bottom edges of the browser window. So the lower right corner of the browser window is the same as the lower right corner of my frame.
- (optional) If the frame content is small enough such that there are no scrollbars or if the page has not been scrolled vertically, then I don't want the image (or <div>) to appear.
- the placement of the image/div needs to take into account the width of the scrollbar(s).
- my focus is to display a button in this lower right corner that, when clicked, will scroll the page to the top.

I found the following script on another site that claims it would do most of this, cross browser, but I was only able to make it work with IE (and I'm using IE 6.0). When I tried it with Netscape 7.1, Firefox 1.0 (Mozilla 5.0) and Opera 7.54, the button didn't float as the page scrolled. I checked browser settings and javascript is turned on for all the browsers.

Can someone point me to a javascript that will do what I'm looking for, or help me understand why the following script isn't working cross browser? I've worked with javascript and the DOM somewhat, but am not a Master of the subject matter, especially when it comes to cross browser issues.

Thanks, and here are the instructions and script that I mentioned above (that I had founed from another site):

Place the watermark on your page where you want it to appear on non-DHTML browsers (say, the bottom). Then nest it inside a <DIV> tag with the attributes id="waterMark" and style="position:absolute". Code: