Hi Anne,
I agree that it can be awkward to have to use the horizontal scrollbar on the permissions screen if your forum is embedded in a page of restricted width - especially when you have added further groups to the standard set.
However, I've come to the view that as it's a screen that one only uses on initial set up of a forum, (before setting a "Redirect" option) and for just a few minutes when adding an additional sub-forum once the forum is running (after redirection is in place), I am prepared to remove the "Redirect" for those few minutes and change permissions in full-width non-embedded window.
Volunteer Helper - but recommending that users move off the platform!
Once the admin for GregHelp now deleted.