I haven't managed to figure what's happening.  According to John Mercouris (Next
developer), the state of CFFI-GTK is rather poor and it will be hard to track
down exactly what's wrong.

Next browser will soon move to another interface which does not rely on cffi-gtk
so it won't be a problem.

Andy, if you have an immediate solution, feel free to chime in, otherwise Next
will have to wait a few more weeks before hitting the Guix repository.

I've merged all the 78 (?) new Lisp packages onto master.
I've moved the Next package draft to wip-next-browser3.

-- 
Pierre Neidhardt
https://ambrevar.xyz/