The possibilities with Firefox multi containers and automation scripts as well are truly endless.

It's also possible to make Firefox route each container through a different proxy which could be running locally even which then can connect to multiple different VPN's. I haven't tried doing that but its certainly possible.

It's sort of possible to run different browsers with completely new identities and sometimes IP within the convenience of one. It's really underrated. I don't use the IP part of this that I have mentioned but I use multi containers quite a lot on zen and they are kind of core part of how I browse the web and there are many cool things which can be done/have been done with them.