Threading was the same in 115. This link include steps to undo threads: https://support.mozilla.org/en-US/questions/1439822 I do not recommend reverting to prior versions, as you will need to move to 128 in time and 128 is receiving regular updates. Also, reverting to prior release sometimes causes problems. One approach is to download prior release and install over the existing release, and then delete the compatibility.ini file in the profile. The officially recommended approach are these steps: # Exit Thunderbird if running. # click windows key and 'r' key # Enter: thunderbird.exe -P --allow-downgrade # click on 'OK'