Here is a quick way that may help you discover an element in your page that may be causing unnecessary scrolling behavior and/or unusual output in your layout:

Put this in style.css:

* {
  background: #000 !important;
  color: #0f0 !important;
  outline: solid #f00 1px !important;
}

 
Here is a bookmarklet which will accomplish this for you on the fly.
 
Earlier I wrote about the usefulness of Vimperator (a Firefox plugin). A great example of its utility would be the ability to create a custom command out of the aforementioned bookmarklet (I chose to call it viewdiv) so that when you type

 :viewdiv 

…. it will activate this useful method. 🙂