I already did:

    javascript:for(var a=document.querySelectorAll('*'),i=0,e; e=a[i]; i++) if (e.currentStyle.position == 'fixed') e.style.position = 'static'; void(0)

I nicknamed the bookmark "fix", so I can just type "fix" in the address bar to fix those pesky fixed elements.

It works perfectly. Well, I vaguely recall there was one site, where it didn't work, don't remember which one (nor cared to figure out why it didn't). At first I was worried that looping over all elements on a page would be too inefficient, but JS is so fast nowadays, there's no noticeable delay. Also, there's no getElementsByStyle method, so I'm not sure how to even go about optimizing that loop.