Retrieving a webpages shows a blank screen when a 4xx HTTP status is returned. Not helpfull.

Hello all,

Using FireFox v52 (last one for XP).

When I retrieve a webpage which returns a 4xx or 5xx HTTP status often all 
that I see is a blank screen without any indication to what is going on (I 
need to open the "Browser Console" with the "Net" tab activated and reload 
to actually see the HTTP status).

Question: How do I get a visible indication of the HTTP status code in a 
case like that ?   Either on the webpage itself, or by way of a pop-up by an 
add-on.

Regards,
Rudy Wieser