As you suggested, I've tried to reproduce this in epiphany and galeon (using metacity), and I can easily reproduce this bug in both of them when viewing pages that use Cascade Style Sheets (I think the address and tabs bars in firefox use CSS also, that is where I found this bug initially).
I'll try to explain it better: when i put some other window (like gcalctool) over the webpage, and I move this window, the webpage part that is redrawn is redrawn displaced. After I set the focus in the browser window again, the webpage is redrawn and the displacement is corrected.
When using compiz, it's harder to reproduce, but I can see something similar when I put the mouse pointer over the "Go", "Google" or "Search" buttons (see white lines in screenshot attached). When I change focus to other window, it gets properly redrawn. This happens when using compiz and metacity.
I'm sorry if I'm not clear enough, but if you need more info just ask. Thanks.