I thought this is clearly obvious, but some people seems to be amazed that I can run four Gmail sessions simultaneously. I even have been accused that I must be faking this screenshot :). No it is not fake, the trick is to run different Firefoxes with different username but all are using the same display. Different user means different cookie set, and different Gmail session.
Follow the these steps to spawn a new Firefox session:
Create a new user if you haven’t done so.
Note the display identifier used by current X session:
Disable X authentication:
xhost +, warning: this will disable authentication for X, this is a security hole if your X allows remote connections (which my Gentoo box doesn’t by default)
Switch to the new user:
su - newuser
Change the DISPLAY variable to match step 1, for example:
Needless to say, this trick will also work for Yahoo, MSN, and all web sites using cookie based authentication that won’t allow multiple logins to the same site.