I recently upgraded to MacOS X Lion. Shortly after that Firefox automatically updated to v6. I began to experience slow DNS lookups.
When you enter a URL into your web browser or click a link to a web page, the first thing it does is ask your DNS servers where that URL points to. Specifically it is looking for the domain name (domainname.com, .net, .org, etc). The DNS server then responds with an IP address which points your browser to it’s target destination which allows the downloading to begin.
For the sake of speed optimization, many websites today use more than one web server to deliver their images and various other files on their pages. One web page may have 3 or more different domains to resolve. If each DNS look up takes 2 seconds, you are looking at 6 seconds of lookup time! Say nothing about the download time. This is why it’s a good to use a service like OpenDNS or Google Public DNS. Often, doing so will noticeably speed up web browsing.
In my particular situation Firefox was trying to take advantage of IPv6 before trying IPv4 which is good and bad. Good for the future of the internet but bad for today’s internet because IPv6 is not in use everywhere yet.
PROBLEM:
- Firefox 6 slow DNS lookups due to priorization of IPv6 over IPv4
THE FIX:
- Enter “about:config” into the URL bar
- Click “I’ll be careful, I promise”
- Enter “DNS” in the filter (just below the URL)
- Double-click on “network.dns.disableIPv6” in the list, setting the value to “True”
- Close and restart Firefox
This dramatically increased the speed of my web browsing. I tested this by enabling and disabling the setting several times just to make sure it wasn’t a network hiccup or somehow related to OpenDNS since I use them.