An extension to add sources is available, but the movie-web version requires excessive permissions that could be unsafe, and it isn't auto-updated, so we'd recommend either avoiding it, or instead using the lonelil version which is a fixed.

https://watch.lonelil.ru/onboarding/extension

Remember to click the extension icon and enable it on the instance you're using otherwise it wont work. The main host (NSBX) may break when the extension is enabled.