Ok, may have scrolled on this page forever. When the page gets lots of content it gets slow. Could you remove the DOM elements at the top as you scroll?
I can't really remove content from the DOM since that would cause other boxes to float back to the top (moving chaos in your window). Maybe replacing the images not in focus with a 1x1 pixel stretched to their size is a fix to decrease memory usage (although I think this will differ between browsers). Anyone here with a good idea how to fix this?