When visiting https://wiki.parabola.nu/ Iceweasel warns the user that the connection is not secure because "parts of this page are not secure". The web console says:

Loading mixed (insecure) display content "http://i.creativecommons.org/l/by-sa/4.0/88x31.png" on a secure page

So the problem seems to be due to a single small image for the CC license adopted by the wiki. Copying that image on the wiki server itself instead of linking to an external unsafe third party would probably solve this problem.