DNS Leaking

Some websites mention that FoxyProxy and other proxy managers leak DNS information. Now I don't know exactly what that means. But it doesn't sound good. Could anything be done about that?

Someone suggested that changing the FireFox key "network.proxy.socks_remote_dns" to true can solve the problem or reduce it. What do you think?

Some links to the discussion of the problem:

http://code.google.com/p/firefox-showip/updates/list

http://code.google.com/u/adura83/updates

A reply by the developer would be appreciated.

OpenDNS

Does using OpenDNS solve, reduce or bypass this problem?