Firefox Profiles – How to Create and Switch Between Them

Here's my situation: I use various web applications like, say, Google calendar, so I log into Google and it remembers me. But my wife also does things with Google apps, like, say, Blogger. I help her out a lot, but to do this I have to log out as me, log in as her, do the work, and then log out and in again. This is very annoying. Is there some way to have Firefox profiles, and switch between them so that each profile has the cookies to remain logged in, so I can work as my wife without having to log in and out all the time.

(I know there is the concept of profiles, but I can't find a way to switch between them in any straightforward way.)