This is a fairly common issue and could be caused by a corrupted folder index. To fix this, you can try right-clicking on the inbox, selecting "Properties," and then clicking "Repair Folder" to rebuild the index. Another possibility is a mouse configuration problem check your mouse drivers and adjust the double-click speed in your system settings, as an incorrect speed may cause single clicks to be misread. Additionally, Thunderbird extensions or themes may interfere with normal behavior. Launching Thunderbird in Troubleshoot Mode (accessible via Help > Troubleshoot Mode) can help determine if an add-on is causing the problem. Lastly, compacting folders through File > Compact Folders can optimize performance, especially if you have many deleted or moved emails over time. If none of these solutions work, creating a new Thunderbird profile might help isolate the issue.
