I'm logged into the main sites for Workplace.SE, Physics.SE, Money.SE, and Space.SE; but show as logged out when I go to any of the meta's for those sites. Attempting to log in again results in the page refreshing with my still being logged out. I am able to visit meta.StackOverflow, and meta.SuperUser. (This is not an exhaustive list.)
This is only happening in Firefox; and I've unsuccessfully tried disabling all my content blockers, restarting the browser, and clearing my cache as suggested in this question; but am still locked out.
On pattern I have noticed: The meta's I can't log into in Firefox are all loading the http site for me; while all the ones that do load are going over https. Those meta's are also not using https when I visit using Chrome; but there I am able to log in anyway.
I tried forcing https on meta.space.SE and got this error in my browser:
The certificate is only valid for the following names: *.stackexchange.com, stackexchange.com, meta.stackexchange.com, stackoverflow.com, *.stackoverflow.com, stackauth.com, sstatic.net, *.sstatic.net, serverfault.com, meta.superuser.com, stackapps.com, openid.stackauth.com, *.meta.stackexchange.com, clc.serverfault.com, meta.serverfault.com, superuser.com (Error code: ssl_error_bad_cert_domain)