IMAP stands for the Internet Message Access Protocol. It enables a mail client (such as Thunderbird) to access messages stored on a mail server. It is more modern and fully featured than POP (Post Office Protocol), which is the other major protocol for accessing mail messages. Most email providers now support IMAP. To see whether your account uses IMAP or POP, check the Server Settings page in the Account Settings.
Thunderbird saves personal information such as messages, passwords and user preferences in a set of files called a "profile".
Add-ons add functionality to Thunderbird or change its appearance. Learn how to install add-ons to Thunderbird.
This article explains how to switch from a POP to an IMAP account in Thunderbird.
This article describes how to install Thunderbird on Windows.
This article presents possible solutions to this problem and workarounds to get Thunderbird updated.
How to update to the latest version of Thunderbird on Windows XP and Vista.
This article will show you how to install Thunderbird on Linux.
This article describes how to install Thunderbird on Mac OS.