Firefox has an even more powerful version of this.
If you start firefox with the "-P" flag you can choose to create a new profile. You can also pass it an argument (e.g. firefox -P default) to choose one.
In this case, the profiles are completely disparate; there is zero overlap. In this case, you simply have to login to one google account per window and paste into the correct window (still not ideal).
To run multiple profiles at once, launch all profiles after the first one with "firefox --no-remote -P <profile-name>". Clicking links will open them with the firefox that was launched without "--no-remote".
How is it more powerful? This is exactly the same thing, but apparently with a worse UI (the multiple profile thing in Chrome is exposed through the UI).
The firefox instances have completely different processes, settings, etc. Everything. Chrome, unless I'm mistaken, does not go that far.
For example, one of my main uses of multiple-profiles is that I have a different profile for every proxy I use. I can launch a firefox profile that's proxied side-by-side with my usual firefox (aside, the firefox proxy settings are exposed via the UI, unlike chrome).
Chrome, I'd have to run "google-chrome-stable --proxy-server=$proxy" and then, again unless I'm mistaken, all accounts will use that proxy server. That, by itself, is a deal breaker.
I'm not familiar enough with chrome's settings and so on to say what does and doesn't leak; I could be completely wrong on all of this, but I suspect I'm correct.
Edit: On looking more, Chrome's does look more complete than I thought. The proxy bit still is a dealbreaker for me (well, and I'm adverse to logging into a google account), but I retract much of what I said.
I haven't used it in a long time, but I did use it at one point.
It's just not as good security and privacy-wise. Using proxies on/off on one profile, as it encourages, results in any tracking cookies seeing both IPs having the same tracking data, and thus your proxy has lost some of its privacy.
I also run entirely different extensions when I'm going for privacy vs fun browsing vs banking etc etc.
If you just want proxies to get around some region restriction and don't really care about the privacy or security aspects, then FoxyProxy might be fine.
I wrote a Firefox extension on 2007 that allowed you to use different accounts at the same time in different tabs (no windows!). The video showing it continues to be available: https://www.youtube.com/watch?v=1EBkB-Yp-zM
If you start firefox with the "-P" flag you can choose to create a new profile. You can also pass it an argument (e.g. firefox -P default) to choose one.
In this case, the profiles are completely disparate; there is zero overlap. In this case, you simply have to login to one google account per window and paste into the correct window (still not ideal).
To run multiple profiles at once, launch all profiles after the first one with "firefox --no-remote -P <profile-name>". Clicking links will open them with the firefox that was launched without "--no-remote".