I hope you can help me understand what is causing this problem in Firefox.

I have a simple log in page with a Lightstreamer listener on it. If I navigate away from the page, then return to it, everything is fine. If I navigate away again the client freezes for several seconds. Eventually I can see in the console a call to lightstreamer/control.js where the request is

Code:
LS_cause     api
LS_op        destroy
LS_session   blah
LS_unique    5
and the response is

Code:
window.LS_lastError = {}; window.LS_lastError[1] = "sync error";
but I cannot fathom out what is causing it. I am not knowingly doing anything with the connection itself during page navigation.