I have tried several times, and re-started Firefox.
Without posting the details of the resource or page, this error message is not actionable.
Confirmed: at that time access to all pages took awfully long or timed out. From Germany at least.
Now it's good again.
I am pretty sure it was a networking issue not related to our server or app.
Sometimes data centers have network issues as does global routing 
I was logged into a server in same data center today and the network was so bad that local DNS would not work.
It was OK not long after.