Latest Windows 10, fully updated Firefox 87 and Google Chrome 89. In the addressbar of FF/GC, enter
https://www.facebook.com. There is zero network activity. GC reports ERR_CONNECTION_RESET, FF reports ns_binding_aborted and PR_CONNECT_RESET_ERROR. Edge opens the page immediately. With cURL (
https://facebook.com) it reaches the site, does a 301 redirect to
www. and the page is returned.
So this is not being blocked at the system level, only at the browser level where FF and GC seem to share the same block list somewhere. Other devices in this wi-fi network can access the site with no problem.
I've disabled firewall for public, private, domain. I've turned off and completely uninstalled Avast. I've disabled every Windows protection mechanism that I can find. I've stopped a number of services that look like they might be related to network activity. I've started others that were Manual/Disabled. Browser cache has been cleared. All addons and extensions have been disabled. The domain is not listed in any local block list that I know of, related to the browsers or otherwise, including in their latest security options related to trackers, ads, etc. The browser security is as disabled as I can make it and ads are not restricted. I've rebooted many times. There is no family protection setting. There is no proxy server, no VPN, no internal DNS.
https://22.214.171.124/ (One of their IPs) reports the connection is not private. That's interesting because it verifies that the browsers can reach the server. The message here is NET::ERR_CERT_COMMON_NAME_INVALID and I can see the DigiCert for *.facebook.com (not expired). So this seems to be related to the domain name and a factor of client-side DNS. "Proceed to 126.96.36.199 (unsafe)" does not work - the host redirects to
www. which cannot be reached. I've used
IPCONFIG /dnsflush. ("Does not work" means the connection failed, not 404.)
What is common to both browsers in this regard? To my knowledge I do not have any custom core network components. Maybe I did something to force a TLS version which Facebook doesn't support. (Just checked FF and set to 1 due to new higher default set in FF last year - no joy.) Following commonly suggested remedies, also set MTU to 1472.