@aw As you can see, https://gnusocial.no runs without Qvitter. Also I have an ugly hack on https://quitter.is for example that presents the non-js version before assuming the client supports javascript.

But as a workaround for !qvitter sites: You can use the /main/login endpoint on any !qvitter site to log in. Then you (manually in the address bar) go to /settings/qvitter and disable it if it was active.

...but as a solution to see the timelines of these sites without logging in, I can't think of any other method than to use the Atom/RSS feeds for individual users as well as the public site, for example: https://quitter.se/api/statuses/public_timeline.atom or https://quitter.se/api/statuses/user_timeline/4.atom
(I can explain how to look those URLs up if you're interested)