Cloud notebooks not loaded / created / open – Mathematica Stack Exchange

I do not know if this is the right place to ask, but I can not offer a better one for now.

The problem is, when I want to open wolfram cloud notebook (by clicking on the "go to code" link in wolfram's alpha responses, or "create a new notebook" here), it does not work. The frame (top bar and center area divided into two parts, one for the input, since I forgot what) appears, flashes and then disappears, leaving the white window without any prompt. The only thing left is a moving blue bar at the top, in the style of modern loading bars indicating that the program is running without any estimate of time.

The problem occurs on Firefox 56 (win7) and 63 (win7 and win10), does not appear version-dependent.

Help me, please.