Hi kpturner,
Usually the popup alert is more a chrome issue than a firefox issue; anyway the popup is part of the connection sharing mechanism: if you do not use the enableSharing call or configure the second parameter to be "IGNORE" (or "ABORT") then you should not see any blocked-popup alert. Obviously that would also prevent pages from sharing their connection.
See
http://www.lightstreamer.com/docs/client_javascript_uni_api/ConnectionSharing.html#enableSharing for the full description