How to do a many-to-many relationship with an intermediate join model with Ember and Firebase

I'm having some trouble modeling these relationships and getting the correct data in my app. I have users, links, and bookmarks. Where bookmarks is a join table so users can have many bookmarks, and links can have many bookmarks

<!-- user -->
export default DS.Model.extend({
  username: DS.attr('string'),
  bookmarks: DS.hasMany('bookmark', { async: true }),
});

<!-- link -->
export default DS.Model.extend({
  title: DS.attr('string'),
  url: DS.attr('string'),
  bookmarks: DS.hasMany('bookmark', { async: true }),
});

<!-- bookmark -->
export default DS.Model.extend({
  link: DS.belongsTo('link', { async:true }),
  user: DS.belongsTo('user', { async:true })
});

In firebase this is what my data looks like:

user
  - userkey
    - bookmarks
      - bookmarkkey : true

link
  - linkkey
    - bookmarks
      - bookmarkkey : true

bookmark
  - bookmarkkey
    - link : linkkey
    - user : userkey

In ember, when I pull a user model I'm able to access the related bookmarks, but not the link that is related to the bookmarks.

How can I fix this?