Can you do a telnet to port 80 on one of let's say Google's webservers? (or any other internet web server)?
Try something like:
telnet www.google.com 80
If this doesn't connect, I'm guessing there is a firewall blocking access to port 80 (on internet sites).
Ping may still work in such a case, since it doesn't use port 80 (HTTP).
If it does connect, it's a browser problem most likely.