Did this a few months ago, somewhat straightforward. A "generic" recipe for any UNIX-based OS would be:

1 - Create a container (Docker, Jails, maybe even chroot)

2 - Assign an ip to the container, NAT to it

3 - Install firefox on that container

4 - Run a SSHD server, enable X11 forwarding

5 - Mount the relevant container's folders to your root fs (eg: map $CONTAINER/.mozzila and $CONTAINER/Downloads to $HOME/jailed-browser/)

6 - Add an ssh config for quick alias

7 - Run `ssh container firefox` and profit

Here's a nice example using FreeBSD jails (I remember following this tutorial, everything worked out fine): https://forums.freebsd.org/threads/53362/

My experience with it, though, wasn't great. X11 forwarding through SSH was quite laggy (even after performing some optimizations on the connection). Good luck if you want to set-up audio/mic support. It's a nice solution for a one-time banking login, not for day-to-day use.