To access your IMAP-enabled Gmail account in Thunderbird:

• Open Thunderbird on your desktop.
• Select File > New > Existing Mail Account. If you don’t see the File menu, you can select the Alt key.

• In the Set Up Your Existing Email Address dialog box, provide your Gmail account information (real name, email address, and password). Thunderbird configures the Gmail connection automatically.

• After choosing Continue, the program will find the correct server details. Then press Done, and a pop-up appears prompting you to log-in to your Gmail account.
• Sign in with your Google credentials.
• Thunderbird downloads your Gmail messages, and you can now access your Gmail on Thunderbird.