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.

Repairing by refreshing works for a very short time. Then I receive what many others have remarked upon. Unable to connect Firefox can't establish a connection to the server at loginprodx.att.net. 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. I am on a Mac, have almost no technical savvy. My Firefox is 38.0.5 I emptied all caches. No history. Nothing. Nothing I know has changed over night. Yet first thing today, I was unable to access ATT/Yahoo email because of the above dialogue. Safari, another browser on my computer, seems to not be affected. The only addon I have is LastPass. Thanks...