The page the query is called on is when viewing a forum thread. In the query I select from the forum_posts table and join the forum_threads table. I'm trying to figure out if I can select data from the forum_forums table to fetch the post/reply permissions.
So is there a way to join the forum_forums table the already joined forum_threads table?
Yes. It's just a matter of joining them on a common field, as you've already done with the INNER JOIN between forum_posts and forum_threads.
Assuming you have a field forum_threads.id_forum, the following should work: SELECT * FROM forum_threads AS fp INNER JOIN forum_threads AS ft ON fp.id_thread=ft.id_thread INNER JOIN forum_forums AS ff ON ft.id_forum=ff.id_forum