I installed thunderbird which required firefox to be be updated to 90.0.2,2. Almost all sites including google.com, americanexpress.com, and mozilla.com to failing loading with:
Your connection is not secure
The website tried to negotiate an inadequate level of security.
www.mozilla.com uses security technology that is outdated and vulnerable to attack. An attacker could easily reveal information which you thought to be safe. The website administrator will need to fix the server first before you can visit the site.
Error code: NS_ERROR_NET_INADEQUATE_SECURITY
Partial upgrades are not supported. Make sure *all* packages are up-to-date or in sync with the ports tree. NS_ERROR_NET_INADEQUATE_SECURITY often appears when "firefox" encounters different "nss" version than what it was built against. IIRC, this is due to TLS defaults not being part of ABI.
Otherwise, I can't reproduce inside poudriere jail with X11/Wayland socket passed through. Provide more details about your environment.
none of the suggested about:config changes made any difference. Doing a "pkg upgrade", e.g. doing all packages fixed the problem for me
Closing per comment 2.