This might be interesting for you people: https://github.com/xnaas/nitter-instances ;-)

Does anyone here know the folks the manage nitter.net and could reach out and ask them to renew their cert?

In the event anyone else was using the Nitter addon, a work around is to instead use the Privacy Redirect addon [1] which can be used in conjunction with the list linked by @sebiw.

[1] - https://addons.mozilla.org/en-US/firefox/addon/privacy-redir...