I can see that there are some servers, which are listed at www.quakeservers.net, are not listed within the built-in server-browser of ezquake. What is the fastest way to add these into the client?

Regards,
toma

Download .txt files from QuakeServers.net and place them to ezquake/sb/. In fact you should only need global.txt since it contains all servers. You can also add qwmaster.fodquake.net:27000 to your master server list if it's not there already. Instructions here.