For developing web sites, I define test domains in /etc/hosts :
I can then access example.org in the browsers.
However I when the Network Manager is not connected to any network, Firefox is not able to access
example.org, it gives an error similar to DNS failure. It cannot even load the localhost, if I try to access it by the host name of my machine - i.e.
I can access example.org, rohit-box, etc. in Chrome. I can also ping them successfully. Thus I have isolated the problem to Firefox.
I am using Linux Mint 13 Cinnamon, Firefox 19.
Edit - I also tried resetting Firefox from the Help menu. The issue persists.