https://github.com/mozilla/multi-account-containers#readme
That one changed my life. It allows me to log into different AWS accounts at the same time. Also different Gmail accounts at once (like my kids' email and mine).
Also it gives you a massive boost in privacy since cookies don't follow you around since they are restricted to one container.
Combined with Container Tabs Sidebar:
https://github.com/maciekmm/container-tabs-sidebar
You get the tree style tabs with automatic organization by container.