You can easily use a firefox profile per account rather than a browser per account and end up in roughly the same boat. Just start firefox with "firefox -P" to

You can easily use a firefox profile per account rather than a browser per account and end up in roughly the same boat. Just start firefox with "firefox -P" to create a new profile, and run "firefox --no-remote -P" on a new instance of firefox and choose that profile to run it side-by-side with your first, but with no data overlapping.