Countries
Read onlyOK here - though I can see a poorly formatted 'please wait while this page loads' really large and feint in the background.
Could only suggest trying on an Incognito window - if that works - then clear your cookies etc on your browser.
It looks like you have ublock running.
I find I have to disable it to get shipping settings to appear.
The Amazon shipping settings page is pretty much the only legit site that is affected in this way by ublock.
I had the very same problem and like you (or so it seems) I was using Firefox.
I temporarily used another browser instead and the shipping settings page loaded correctly.