Is it possible to add styles to visual editor iframe in wpforo?
In wordpress it is done by add_editor_style function.
This is the WordPress editor. wpForo doesn't have separate editor. Just try it.
I did try it.
It works best at creating pages and posts [back-end] but minor features addition to the front-end of the forum.
There is no conflict with wpForo. I did not install it yet on my live site.