Under HTTPS everywhere, now the comic has transitioned from being blocked in firefox (due to some insecure content) to seemingly an infinite redirect loop, though it is hard for me to tell what is actually going on. In any case, only half the page loads, and the security icon quickly switches back and forth between the "everything is secure" icon and the "secure page with some insecure elements blocked" one.
UPDATE: It seems that the loop is caused by a change to how the site handles https requests. On this comic, it automatically switches to http when given an https request. The unfortunate thing is that HTTPS Everywhere tries to turn that back to https, and they keep fighting each other and never end up loading the page over either protocol. This is not a hard problem to fix (by just turning off the rule for xkcd.com in HTTPS Everywhere) but maybe it could be more elegantly fixed by getting a certificate for linden0.xkcd.com.