Boris Zbarsky <bzbarsky@mit.edu> has asked Johnny Stenback <jst@mozilla.org>
for superreview:
Bug 313217: document.open('replace') now opens text/plain document where it
used to open text/html
https://bugzilla.mozilla.org/show_bug.cgi?id=313217

Attachment 200309: Patch to make a type of "replace" mean HTML but not replace
https://bugzilla.mozilla.org/attachment.cgi?id=200309&action=edit

------- Additional Comments from Boris Zbarsky <bzbarsky@mit.edu>
Just treat "replace" in the first slot as if nothing were set.