No mention of OTR. :-( When your client is a Web app on a trusted server (i.e. OTR key on the server), you could avoid multi-client issues by having only that on XMPP client that you connect to from multiple browsers.
Came here to say just this. I've been looking for a replacement for our Openfire server for some time now, but there just hasn't been anything that's quite there yet.