Ironically, the thing that drove me to Firefox was the excellent Account Containers system that I found necessary to manage being logged into multiple Google Apps accounts simultaneously (I have five ). Each tab owns one account — that way, Google Drive files from my work don't randomly refuse to open because I'm also logged into my personal account. (Chrome has no solution for containing accounts across tabs, last I…
What does that mean in terms of resources? Is 2 FF tabs that much less taxing than 2 Chrome instances? fwiw, I use multiple Chromes, each with its own project / client, own password manager, etc. I don't think I could maintain the silos I do with FF. I wish I could sack Google (Chrome) but I can't, afaik.
You can type "about:profiles" into the URL-bar to manage your profiles (which you can also bookmark for easier access).
You can also run "firefox -P" in a terminal to access a similar GUI. With "firefox -P profile_name", you can start a specific profile. To run multiple profiles in parallel from the CLI, you have to start further profiles with "firefox -P profile_name --new-instance" (Linux) or "firefox.exe -P profile_name --no-remote" (Windows). This is because when you click on a link in an application, it needs to know in which browser instance to open that link.
As for resource usage, the profiles separate everything. Browsing history, bookmarks, logins, add-ons etc. It's essentially like a second Firefox installation. This also means that it actually runs two instances, so twice the RAM usage and somewhat more CPU usage to move that data around.
The Container Tabs on the other hand only separate what needs to be separated in order to look towards webpages like two different browsers. So, there's a different cookie jar, different localStorage, different HTML5 Web Storage etc., but other than that it's the same as just opening two tabs. So, probably not even 1% more RAM usage than using Firefox without any separation.