@unman this used to work but it is no longer the case. From what I’ve read, due to the threat of the browser’s profile being used for identification attacks (edit: see discussion on Customizing Firefox in Disposable VMs - #28 by QubicRoot), the profile is generated from scratch when tor browser boots in the DVM. Try it yourself.
It totally breaks the usual Qubes customization workflow and expectation about how we can persist configurations.