If you're really this serious about security, you should be using Qubes OS. Then, a browser choice stops being important, since the strong isolation would prevent an exploit to do any damage. And disposable VMs allow to do insecure staff without any risk.
Xen is not an obscure system. Hardware isolation was broken last time in 2006 by the Qubes founder ("Blue pill software").
I open my email in a dedicated VM, so only my email provider could attempt to compromise me. Attachments are automatically opened in another, disposable VM.
I talk about the distro qubes os and not about xen.
Also my email account and everything normal I do, is part of my normal life and it's very helpful to be normal.
If I would ever do something out of the ordinary and want to do something which requires physical access, it's much easier to travel the world as someone who has a normal Internet profile.
My personal data is protected enough on Gmail and gdrive.
