I'm seeing the following exception in FF 3.5.6:
uncaught exception: [Exception... "The URI is malformed" nsresult: "0x804b000a (NS_ERROR_MALFORMED_URI)" location: "JS frame :: http://x :: refreshPage :: line 193" data: no]
This error occurs when calling document.location.replace("/relative/url") on the parent window of an iframe.
It's also reproducible in FF2, but IE8 doesn't exhibit the problem.
EDIT: The following code in the same context doesn't have the problem:
document.location.reload();