[Bug 17743] When setting designMode to 'on', the selection should be moved to an empty selection at the start of body (or something like that). If there isn't a body yet, wait until there is. Don't do this for contenteditable.
[Bug 18045] Based on my experience and from reading many questions on the Web, this API is seriously flawed. It treats cross-domain iframes the same as same-domain iframes, except that almost every operation on contentWindow is an error.