One important feature other privacy VPNs offer is the ability to use proxies for per-service split-tunneling. For example, when using the Firefox Multi-Account Containers extensions, one can assign different HTTP or SOCKS5 proxies for different containers. This allows users to compartmentalize multiple online identities by assigning a different IP address to them. Some desktop apps also support specifying a proxy.

Proton has already stated that SOCKS5 won't be supported because it doesn't meet some security requirements. However, Proton already operates HTTPS Squid proxies, because they are used by the Proton VPN browser extension.

These HTTPS Squid proxies require authentication though, because the Proton VPN browser extension is designed to be usable without the desktop app, and it needs to check whether the user has access to Plus servers. The extension uses a temporary session token for authentication to the Squid proxy, so this can't be replicated manually when setting a Firefox container / desktop application to use a proxy.

I request that unauthenticated access to the HTTPS Squid proxies without the temporary session tokens should be allowed if the user is already connected to Proton VPN via the desktop app, and thus has already authenticated themselves.