said by no__1__here:Agree on both counts.
Firefox can run multiple profiles concurrently. The "trick" to keeping the sessions from sharing is the -no-remote flag. For example...
firefox.exe -P myotherprofile -no-remote
...will launch Firefox with the "myotherprofile" profile.
Another option (one that I use more often) is to start your browser of choice in a separate Sandboxie sandbox.