The DNS server is not set by the browser, it is set by your network connection and is an address pointer to a server located out on the internet. Many ISPs maintain a DNS server for their customers so you may be set to point to a DNS server your ISP hosts. But if you don't like your ISPs DNS server you can always change your network connection to instead use one of the big common DNS servers available from huge online presences such as Google.
FYI: A DNS server is just an address converter. It converts words like
www.google.com into an IP address such as 8.8.4.4 so your browser can actually get to the server located on IP address 8.8.4.4
See video
>>HERE<< on how to change your DNS server & backup DNS server to Google's DNS servers.
Once you have updated your network settings, Run CMD.EXE and in the window type in:
ipconfig /flushdns
... and hit <enter>.
Your DNS information should then be rebuild w/in a few minutes w/ the info from Google's DNS servers.