I've experienced the same thing in the past - it's normally due to a crappy router (acting as DNS server) not supporting IPv6.
What's happening, is that for every name lookup, opera & firefox are attempting to resolve via IP6, waiting till it fails (aprox 30 seconds per lookup), then trying again with IPv4.
didn't work for me either.
There's a couple of possible solutions.
1) Upgrade the router (or the device that's providing DNS lookups).
2) Disable IPv6 lookups in Firefox. Enter about:config
in the address bar. Find network.dns.disableIPv6
and set this to true
. There is, AFAIK, no equivalent for Opera.
3) Overide the DNS lookup settings in /etc/reolv.conf
to use different DNS servers, such as OpenDNS
(which is what I ended up doing at the time).