Is it within the same thread it's different sizes? Or the whole page changing until you go to another page? If it's the whole page, is this only happening on e-Hell? Or are other sites affected too?
Are you using a scroll wheel on your mouse to scroll through the page? If so, is it possible you're hitting a button on the keyboard at the same time? I know if I hit Ctrl and use the scroll wheel, it changes the zoom on the website I'm on while I'm at work (Chrome, Windows 7). I know there's ways to do it at home (Flamingvixen, Mac OSX), but I'm not sure the exact combination of keys.
Sorry, not trying to bombard you with questions, and I don't know anything about the back-end code on the site, but if it's something simple like your browser or buttons you're bumping and not realizing it, it's a simple fix.