This profile will be used automatically unless you invoke the Profile Manager and create a new profile. When you install Thunderbird it creates a profile called 'default'. Second, it stores any changes you make while using Thunderbird (for example, changes to account settings and changes to the toolbar).
First, it stores your local mail, and possibly copies of messages that reside on the mail server (depending on your account configuration). In Thunderbird, the profile stores two main sets of items.
