How to separate work projects on Mac?

I am currently working on very different projects, from multiple software projects (where I spend most of my time in the shell, using zsh and vim) to writing (vim + some other tools) to consulting (some shell, a lot of Firefox). In all cases I need some browser running.

What I really love is having separate histories and sessions both in the shell and in my browser.

For now what I ended up doing is:

* use the same mac user

* [works ok] use iTerm profiles, and set different environment variables / launch commands for each iTerm profile notably to change shell history files

* [works ok but needs trickery] use tmux + plugins + iTerm for saving shell sessions

* [works bad] separate Firefox profiles.

I wonder what other people are doing on that?

From where I stand, I feel like using separate Mac users for each project is the best bet, as per simplicity. I feel it'll have the added interest of better psychological separation of projects (different desktop, etc.). But will need a heavier setup (notably: synching dotfiles).