window.onload Problem

The window.onload Problem - Solved!
によれば、

The problem is that the onload event fires after all page content has loaded (including images and other binary content). If your page includes lots of images then you may see a noticeable lag before the page becomes active. What we want is a way to determine when the DOM has fully loaded without waiting for all those pesky images to load also.

ってことで、ブラウザ毎の回避策が書いてある。