"Firefox can’t establish a connection to the server..."
I am having trouble accessing to certain websites using my MacBook Pro. The screen shows:
"Unable to connect
Firefox can’t establish a connection to the server at www.ncbi.nlm.nih.gov.
The site could be temporarily unavailable or too busy. Try again in a few moments. If you are unable to load any pages, check your computer’s network connection. If your computer or network is protected by a firewall or proxy, make sure that Firefox is permitted to access the Web."
Can someone please help?