I haven't seen this info in Firefox before, it may be something new in latest version Firefox 51.0.1 (on Windows 7).
I checked why there is orange rectangle beside lock in address bar and to my surprise new info is "This page uses weak encryption". Looking in details it is AES-128 using TLS v1.2.
But looking at ssllabs.com test to see what is wrong and there is grade A without anything wrong at all.
Any idea what Firefox is trying to tell us?
ssllabs.com result (click on image to enlarge - it can take several seconds to open: