If you switch your fonts to be the same, I think you'll find that this rendering behaviour exists in both. This is because this webpage is a bit ecclectic with how it lays out its elements.
** Changed in: firefox (Ubuntu) Status: Needs Info => Rejected -- rendering issue with ubuntu firefox, doesn't reproduce on offical builds https://launchpad.net/bugs/49124 -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs