There is one thing you can do about it!  Make a positive bookmark for that same story (if you’ve read and liked it).  Tell your friends to do the same.  20 bookmarks and that ugly review will vanish from the first page, and that means SO MUCH to authors, as does seeing positive bookmarks.

You can’t stop this user from leaving their bookmarks.  AO3 is pretty neutral, by design, and that means bad things as well as good things.  There’s a reason you can’t directly message users, and it’s to stop flame wars and abuse.

But you can take action one story at a time.  Knock that ugly bookmark back a few pages.  Tell the author that YOU like the story and share it with your friends.  Leave a positive bookmark of your own.  And out in the community (tumblr, twitter, wherever you hang out), be sure to preach that bookmarks should be either positive or private.

Tab Joey is a modified tab-it. It makes it easier to remember why you bookmarked a page.

The intent to bookmark a page is usually to come back to a specific piece of content on that page.’Tab-it/Post-it’ bookmarks are not very contextual in this respect.

While one can bookmark a page, you have to scribble in your books to mark that one picture or that one sentence that you want to come back to.