I've had occasions when I needed to login to multiple Yahoo accounts at once. I used to do this via multiple pcs or via virtual machines (vm). Recently, I read about using firefox profiles and I decided to look into it. I've used this and really like it. I configure my firefox profiles with different skins, which helps me determine which session I'm on.
To setup multiple profiles use the below command in Windows -> Run:
To run using the profiles you setup use the -no-remote option like below.
firefox.exe -P default -no-remote
firefox.exe -P meebo -no-remote
I have two profiles setup. One for Meebo, with its own skin, the other is my default firefox interface. Click this link for more on Firefox profiles.
Do you use firefox profiles? Do you use them simultaneously like I do?