The Thunderbird update failed error normally occurs because some other copies of Thunderbird are running on your computer. You can fix the problem by using the steps mentioned below and running the update as admin:
• Step 1: Close the Thunderbird process in Windows Task Manager.
• Step 2: Restart the computer so that no Thunderbird processes are active.
• Step 3: Open the Windows Start Menu and type thunderbird in the box.
• Step 4: Right-click on the “Mozilla Thunderbird” option that appears.
• Step 5: Click the ‘Run as Administrator’ option and press ‘Continue’ if the User Account Control dialog comes up.