Firefox 1.5.* is affected by a bug that prevents the browser from automatically redirecting a page request with HTTP return code 302 (Moved temporarily) in case the request is issued through XmlHttpRequest and the document.domain has been set.
Instead, the XmlHttpRequest call returns with a 302 error code.

See bug 337453 at

This bug does not casue any issue to Lightstreamer. But if you perform your own XHR calls together with Lightstreamer (that sets the document.domain) and HTTP redirection is needed in order to reach the final page, then your request may fail.

This bug is currently in "unconfirmed" state, so it seems that it has not been faced yet.