As brought to my attention by Max, through a post on his talk page: https://meta.wikimedia.org/wiki/User_talk:MZMcBride#HTTPS_switch
== The problem ==
Basically, some user defined JS out there has "http://" hard coded, and when you request insecure (non-https) resources during a secure session you get errors in many modern browsers.
This is a heads up that this user created code might need some special attention before and after the switch over.
== How to fix ==
The best option is to use "protocol relative" urls, these are urls that start with "//someurl" instead of "http://" or "https://" or "gopher://" etc.
Here's a blog post about when we started using protocol relative urls in MediaWiki and at WMF: https://blog.wikimedia.org/2011/07/19/protocol-relative-urls-enabled-on-test...
I've put up basic instructions on the HTTPS page on metawiki: https://meta.wikimedia.org/wiki/HTTPS#Help.21_My_code_is_broken.21
Thanks for getting this out to the appropriate channels!
Greg
cc'ing Wikibots-l@lists.wikimedia.org because there might be some overlap of affected people on that list.