I've looked at the AO3 issue a bit more, and frankly it looks like they have a bit of an interface bug at the moment.
If I go to a story URL (when not logged in), such as
http://archiveofourown.org/works/7214746, it warns about the evils of "adult content" and gives a Proceed button. There's also fine print about "accept cookies...will not be asked again".
When I click Proceed, it goes to
http://archiveofourown.org/works/721...iew_adult=true, like it used to. But then it immediately redirects to the first chapter URL (
http://archiveofourown.org/works/721...pters/16372990) where there is another warning about the evils and a Proceed button to go to the same chapter URL with ?view_adult=true added.
And every time you click to a new chapter, you get yet another warning about the evils and a Proceed button. Apparently their cookie mechanism is broken.
That's not an ideal desirable user experience, so I expect that AO3 will realize that and do something about it.
And I don't want to change FFF to match the current behavior when I have reason to expect them to change it again. I'll look into it again tomorrow.