New rules for fanfiction sites
Several fanfiction sites support https, but don't redirect to the https site. fanfiction.net (with or without www) should redirect to https://www.fanfiction.net/ . m.fanfiction.net should redirect to https://m.fanfiction.net/ . fimfiction.net (with or without www) should redirect to https://www.fimfiction.net/ , and the static content subsite fimfiction-static.net (with or without www) should redirect to https://www.fimfiction-static.net/ .
Note that some mixed content exists due to content linked in from offsite sources, but no active content as far as I can tell, only images and similar.
To upload designs, you'll need to enable LFS and have an admin enable hashed storage. More information