Since I'm using mozilla on linux laptops, /etc/resolv.conf is often changed by getting DHCP leases from different networks. Since Mozilla seems to cache IP address of DNS server only at boot time, Mozilla can't resolve URLs after such an update of /etc/resolv.conf if the cached DNS server address is not reachable. For example, If I boot mozilla at my office, DNS server address, which is 192.168.1.1, is cached. When I go home, or go to conference room with wireless LAN card, my laptop gets new DHCP lease but Mozilla does not update cached DNS server address. If 192.168.1.1 is not reachable from there, Mozilla no longer resolve URLs and I have to restart it.