local websties are not working when internet connection is active

Hello,

I've just upgraded my Fedora to 17 on one of my computers for testing.
I work as a web developer, so I have a couple of websites set up locally.
Now whenever I try to access them from firefox on my laptop while internet connection is active, I get an error that they cannot be found. As soon as I disable the internet connection, they work flawlessly. As soon as I re-connect and reload, I get an error "website not available". Any ideas anyone?

Many thanks,
Marek