odd. i thought my :firefoxnightly: had lost all my existing tab-notes, which wouldn't have been a catastrophe but would have been disappointing. on a whim i thought to recheck about:config for its current boolean value of my previously manually-enabled browser.tabs.notes.enabled, & thus found it had reverted to false during some very recent update. i flipped it back to my desired true, & voila, my existing tab-notes are once more visible & editable, with new ones "creatable".