Disabling certain keyboard shortcuts in Thunderbird


Hi - does anyone know how to disable (or reassign) the single key keyboard shortcuts in Thunderbird?  If keyboard focus is not in the email, then every key typed that has a corresponding single keyboard shortcut gets activated.  For example, if I select "a" , whichever email was previously selected would be archived into an offline folder.  Obviously would rather keep combination shortcuts like Ctrl+C to copy (and paste). 

Not sure why sometimes focus is automatically shifts to the email but sometimes it stays with the main view.  Bad enough to lose the email text that was not captured but then to realize that I have been activating unknown functionality then trying to figure out what was typed to undo whatever the system just did.

Appreciate any ideas or suggestions!