I am running the latest version of HTTPS Everywhere for Firefox. See website here: https://www.eff.org/https-everywhere .
I'm using Firefox 25.0.1 on Kubuntu 12.04.
If HTTPS Everywhere is active, I cannot log into http://meta.unix.stackexchange.com . If I disable the extension I can log in. Obviously, I prefer to keep the extension active. I have never had issues at any other sites other than meta.*.stackexchange.com.
This makes me much less inclined to log in and participate in meta discussions because there is a barrier to doing so (and that barrier involves restarting my browser).
Maybe a greasemonkey script or something would solve this??? (I have no idea...)