after installing latest FireFox update my internet connection now cuts off when I connect to VPN
I just downloaded latest FireFox update. I immediately lost my internet connection. I disconnected my Proton VPN and my internet access was restored. I reconnected the VPN and again otherwise lost internet connection. I was not having problem before update.
Then the problem is the VPN connection. As you said with VPN off it works fine. So the issue is with Proton VPN.