If you have ever experienced "stalling" issues with firefox, such as typing in an address, or clicking a link in a stores shopping cart to go to a new product page etc, and having the connection either time out, or take incredibly long try this.
go to about:config in the URL address field.
Scroll down to network.dns.disableIPv6 and change the value from false to true
go to about:config in the URL address field.
Scroll down to network.dns.disableIPv6 and change the value from false to true