Hi,
In a perfect world the browser should close the connection when you close the tab.
Unfortunately I can recall there were cases when the connection was left pending, that's why we introduced a hook in our demos to manually close the connection upon page unloading.
see
https://github.com/Weswit/Lightstreamer-example-StockList-client-flex/blob/master/Flex4_StockListDemo/src/Flex4StockListDemo.mxml#L168
and
https://github.com/Weswit/Lightstreamer-example-StockList-client-flex/blob/master/Flex4_StockListDemo/deploy/Flex4_StockListDemo/index.html#L111
Anyway if the connection remains open the server will detect the issue after a while and eventually close the connection.