Hey all, thank you for your replies.
The problem was not only with FireFox but also with Internet Explorer. I thought that it might be the problem with my internet connection. It was an horrible experience to be without an Internet
I tried to figure out what was wrong which took a long time though. Well.. finally, I am now connected
I restarted FireFox... no go...

then I restarted computer and Oh! It worked
Thanks again for your help guys!