How to Disable DNS Prefetching in Firefox 3.5

If you just upgraded to Firefox 3.5 and have been frustrated with many "server not found" error messages, you might be having trouble with a new feature introduced into the 3.5 version of Firefox called DNS prefetching. DNS prefetching looks up every link on a web page and figures out where that link is going. This is supposed to speed up web browsing. Obviously if you're getting a lot of "server not found" messages, DNS prefetching is really slowing you down. This feature needs some work. Until it's fixed, you can disable DNS prefetching in two ways:

• Open Firefox 3.5.
• Type "about:config" into the address bar and hit enter.
• Click "I'll be careful, I promise!".

This "about:config" menu is where users can make changes to Firefox's configuration.

• In the "filter:" bar, type "prefetch". This search should bring up one result: "network.prefetch-next".

You'll see in the "Value" column that this preference is set to "true".

• To disable DNS prefetching in Firefox 3.5, simply double-click the gray line to switch this value to "false". This new setting is now saved and should take effect immediately. If you ever need to turn DNS prefetching back on, just do all these steps again but set the preference value back to "true".

• If you are still getting lots of "server not found" error messages, you can close Firefox and restart it.
• If you are still getting lots of errors, you can restart your computer.
• If you still getting lots of errors, there is another setting you can try.
• Open Firefox 3.5 and go to about:config as described above.
• In the filter bar, type "network.dns.disablePrefetch".
• There should be no search result.

There is no search result because you will have to create this setting.

• Right-click in the blank search result area.
• Highlight "New" and then click "Boolean".
• Type "network.dns.disablePrefetch" into the space. Hit OK.

• Choose the value "true" and hit OK.

• To confirm that you created this new setting, type "network.dns.disablePrefetch" in the about:config filter bar.

If you created the setting succesfully, it will show up in the search area.

• If you are still getting lots of "server not found" error messages, you can close Firefox and restart it.
• If you are still getting lots of errors, you can restart your computer.
• If you still getting lots of errors, then you might want to consider uninstalling Firefox 3.5 and installing Firefox 3.1, which did not included any DNS prefetching features.

Other resources: This Mozilla article about controlling DNS prefetching in Firefox 3.5