That doesn't sound like a Firefox setting. I searched for that message and found a screenshot with "Watchguard Technologies, Inc." on the bottom. Does yours have that?

WatchGuard is a firewall company. The following is an example help article on this kind of block. I assume it is caused by the website's firewall settings and not yours:

https://www.watchguard.com/help/docs/help-center/en-US/Content/en-US/Fireware/services/geo/geo_about_c.html

Can Safari get around it?

If your location is blocked for whatever reason, you could try using a VPN as a workaround.

Are you using a VPN?

What do these websites say about your location?

http://whatismyipaddress.com/ Under the map, look for Location Not Accurate?

http://browserleaks.com/geo

https://whatismyipaddress.com/geolocation

https://html5demos.com/geo/

https://www.iplocation.net/find-ip-address

How to set your location manually in Firefox(Windows) https://support.mozilla.org/en-US/questions/1197142#answer-1115502

https://support.mozilla.org/en-US/kb/does-firefox-share-my-location-websites

If your location is blocked for whatever reason, you could try using a VPN as a workaround. Are you using a VPN? What do these websites say about your location?

Do not tell me to use a VPN. I want to be able to modify whatever setting is blocking this country.

Fred the OP does not want to use a VPN as said in OP. The OP is in Canada and wants to view a US website that is blocking perhaps all IP's outside of US.

I want to be able to modify whatever setting is blocking this country.

I agree with jscher2000 that this may very well be due to the website doing in perhaps blocking all IP's not located in the US.

A VPN may be your only option though a proxy could work however it may be slow and is not really not secure or private, especially depending on what one you use.