https://support.mozilla.org/en-US/kb/rebuilding-global-database
Steps to Rebuild the Global Database
Quit Thunderbird.
Locate the global-messages-db.sqlite file in your Thunderbird Profile.
Delete the global-messages-db.sqlite file.
Start Thunderbird. The re-indexing process will start automatically. Depending on the number of messages, it might take some time for the indexing to complete. You can continue to use Thunderbird, but performance might be affected and search will return only partial results or even no results until the indexing is complete. The indexing progress can be monitored through the Tools > Activity Manager menu.
How to find your profile
Click on the menu button or menu bar.
From the Help menu, click Troubleshooting Information.
In the Application Basics section, Profile Folder, click on Open Folder.
The Windows Explorer window will show the name of the profile as well as the path to it.
