Chrome makes it quite a bit easier with multiple user accounts - go to settings, scroll down, and add a user. You can run multiple at the same time (each gets its own window, can spawn new ones, etc), and they all have separate settings, extensions, etc. Very highly recommended if you're a Chrome user.
If you're on Firefox... seems like they only really care if you use their Profile Manager, which is a horrible alternative, but it does work reliably across all versions as long as you never ever ever launch the browser directly.
Or if you don't mind rewinding time a bit, and using OSX, http://www.stainlessapp.com/ (assuming it still works) has a brilliant idea: bookmarks can be associated with sessions. Have one for each account, run them all side-by-side in tabs, and it works great. I wish every browser would do this.
If you're on Firefox... seems like they only really care if you use their Profile Manager, which is a horrible alternative, but it does work reliably across all versions as long as you never ever ever launch the browser directly.
Or if you don't mind rewinding time a bit, and using OSX, http://www.stainlessapp.com/ (assuming it still works) has a brilliant idea: bookmarks can be associated with sessions. Have one for each account, run them all side-by-side in tabs, and it works great. I wish every browser would do this.