I was using my computer, went to the store so I hibernated it, came back about an hour latter, and woke it up, and when I tried to visit a page from all my tabs I had open, I got an apache port 81 error, saying firefox could not open a site.
Maybe it was your Wi-Fi. or wired network connection which disconnected, and can't connect again, or your router/modem did not give you a new IP to go online.
Restarting your computer may fix the problem.
Port 81 sounds like a port you use to connect online with web browsers.