About this Add-on
Please note that the 'T' key is by default assigned to the menu item 'Go > Next > Unread Thread': this key assignment will be replaced by 'Shift+T'.
Although the add-on is now restartless, there seems to be a problem in Thunderbird that a key that has been used stays active, even if it is changed later by the add-on. If this happens, you'll have to restart Thunderbird to get the keys working correctly again.
This also applies if you remove or disabled this extension.