How to start Firefox using two different profiles at the same time?

Solution 1:

For that I use ProfileSwitcher.

About this Add-on:

This extension makes easier to use more profiles in Firefox and Thunderbird. It adds in the File menu two new items to start another profile or the profile manager. From the extension's preferences, you can choose what to do when you launch another profile (close the one in use, don't close it, ask every time - If you choose to run the profile manager in safe-mode, the current profile will be always closed). Moreover it adds the name of the profile in uso in the titlebar (on Thunderbird) or as tooltip in the statusbar or in a panel in statusbar (on Firefox) or as icon in statusbar