Hi!  Thanks for the feedback.

> M-x
> scroll the list to the bottom (with down-arrow) (freezez at
> JUMP-TO-HEADING)

I can't reproduce this.  Can you produce this systematically?  Can you post the
content of /tmp/next-gtk-webkit.log?

> “next-gtk-webkit” is not responding."

Where do you see that?

Note that next-gtk-webkit is quite stable on its own, the issue is with
WebKitGTK.  I still need to tinker with it a little, and hopefully the situation
will get much better.

> navigate to some page on youtube
> press play and seek (freezes when trying to seek)
> (gstreamer, clutter-gst, gst good, base libav installed)

Can you play any video?!?  I can't play any video at all on GuixSD.  I works on
Arch Linux though.

Currently, I've setup the following workaround in ~/.config/next/init.lisp to
play videos with mpv.

--8<---------------cut here---------------start------------->8---
(define-command play-video-in-current-page ()
  "Play video in the currently open buffer."
  (with-result (url (buffer-get-url))
    (uiop:run-program (list "mpv" url))))
(define-key *global-map* (key "C-M-c v") 'play-video-in-current-page)
--8<---------------cut here---------------end--------------->8---

> I tried it out for some time now. Unfortunately it is buggy and freezes
> on me with no backtrace provided :-/.

Stay tuned, next release (hopefully by next week) will be much, much better!

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