Another little beef with firefox - it doesn't figure out the size of images first (like IE does) and move all the crap around on the screen before it's loaded - The result is that viewing an image-heavy page causes the text to fly and scroll all over the place, so you have to wait for every image to load before you can read anything.
If that's the only reason you're not using Firefox, it's a fairly minor one.
This is not the exact thing you're talking about, but you can have Firefox display images as they load instead of placeholders like it normally does.
There are various ways to set an advanced preference... I prefer this method:
1) In the address bar, type "about:config"
2) Find the setting"browser.display.show_image_placeholders", or if it doesn't exist, add it, type boolean
3) Set it to false.
Now then, keep in mind that the thing you describe is caused by image tags that don't have widths and heights pre-set... This affects BOTH browsers equally. Are you sure you're not just viewing different websites in IE and in Firefox?
EDIT: The fix I posted above will HELP the issue, as as soon as images start loading the browser will know how big they are.