Bookmark app is not working properly in mobile.
Is it possible to have a bookmark button on each post instead of floating bar.
Can you share a link to your site?What kind of mobile device and browser you're using?
As to your question. If by "post" you mean timeline posts then unfortunately no, we can't affect the way posts are rendered or their actions available. But you can open any post in a new window and bookmark it this way on its page.