After using FB 6.1 and 7.0 it suprises me that the same bug is still present.
Everytime i enter a "faulty" ie. non-existing DNS name ie "www.express.se" it completly hangs all open Mozilla windowses and maintains this state for up too 2 minutes.
Havn't got around too trying this with a direct connection too the internet but it is very irritating that this really simple function as DNS resolving should hang all open browser windowes for a period of time.