[sf-lug] Firefox 77.0.1 rejects sendgrid URLs.

[Michael Paoli]

> From: "Bobbie Sellers" <bliss-sf4ever at dslextreme.com>
> Subject: [sf-lug] Firefox 77.0.1 rejects sendgrid URLs.
> Date: Wed, 10 Jun 2020 14:59:41 -0700

>     Anyway to figure out why I keep getting these remarks instead of
> a connection.
>
>> Unable to connect
>>
>> Firefox can’t establish a connection to the server at  
>> u1584542.ct.sendgrid.net.
>>
>>     The site could be temporarily unavailable or too busy. Try  
>> again in a few moments.
>>     If you are unable to load any pages, check your computer’s  
>> network connection.
>>     If your computer or network is protected by a firewall or  
>> proxy, make sure that Firefox is permitted to access the Web.
>
>     Now I can load lots of other pages but anything with the  
> sendgrid prefix as seen
> above stopped going thru after the recent update.

So, perhaps it's an issue with sengrid.net., and not at all specifically
Firefox?
Any way to figure out? ... yes, many.  In general, do logical
divide and conquer.  E.g. try to split the problem roughly
in half, test each half.  Repeat as needed for any portion
that fails.
So ... did you try other ways to connect?  Did you try other
browsers/clients?
Did you try from other source IPs/locations?
Did you try at other days/times?
And the results were?  ... what?

I'm able to connect fine:
$ nc -vz u1584542.ct.sendgrid.net. 443; nc -vz u1584542.ct.sendgrid.net. 80
Connection to u1584542.ct.sendgrid.net. 443 port [tcp/https] succeeded!
Connection to u1584542.ct.sendgrid.net. 80 port [tcp/http] succeeded!
$
You specified neither port nor protocol, so I'm presuming customary
defaults of https on 443, or http on 80.
In any case, both connected fine for me.