Moving with my notebook computer from one WLAN to another (in another part of the building), either closed (thus in "sleep mode") or not closed, very often results in a loss of all connections. FF says that it cannot find the servers any more, while a direct "ping" or other softwares have no problem seeing and connecting to the servers.

I tried different proxy settings, but this did not change the situation. Normally the only "solution" is to close or "kill" the firefox, and after a new start also the FF finally "gets it" properly.