I have the following suggestion as a forum user.
If I am not mistaken, right now it is only possible for a forum user to select only the question itself as one of her favorites.
I would love to have the heart icon for the comments and answers as well. Because sometimes I really like not the question but the answer or comment itself. ( it may have additional info not much related to the question itself and I prefer directly look at it later on without searching it through the comments).
I would appreciate if you can consider this.