I made some progress with popups under IE.
1- The content of the inner document still shows about halfway across the iframe under IE6 through IE8.
I found that if I set 'position: 0px' instead of 'relative' for 'content.css' in SF_popupform.js (line 233) - the content is displayed correctly both in IE and Firefox (I haven't looked at Chrome yet).
2- Something is terribly slow in SF_popupform.js under IE.
- Laurent Alquier