How can you enforce that an Browser can only access specific Domains in an AppQube?

[moonscape]

You might have a look at this guide:

Restricting a qube to selected websites

A common requirement seems to be the ability to restrict a qube’s access to a certain subset of websites; something that is difficult to achieve using the firewall rules due to multi-hosted websites/CDN’s etc. The following is a description of one way to setup a qube with restricted website access using only software that is already installed in Qubes OS. Create a qube based on template:fedora-32 or fedora-33, lets call it my-proxy. Set its networking to sys-firewall. [Screenshot_2021-03-12_1…

As alternative install host-based application firewall OpenSnitch, if you want something GUI-based and no extra proxy qube. OpenSnitch might as well be installed in a proxy and can control all connections of qubes, which have this proxy as netvm.