My theme was not centering in firefox, but it was in ie. I searched for quite a while, and found a solution here where someone suggested to add <div align=center> in the header and close it in the footer. This works as can be seen at http://www.dryfly.ca. Without this code, the page gets left aligned in firefox (but is okay in ie).
However, this code does not validate. Does anyone have any other ideas or suggestions on centering this theme?