See
Issue #155 (UXP)
You can fix it by manually editing those files:
chrome/linky.jar:context/main.js
Line 841
from:
const linkyContext = new LinkyContext();
to:
var linkyContext = new LinkyContext();
chrome/linky.jar:context/options.js
Line 17
from:
const linkyOption = new LinkyOption;
to:
var linkyOption = new LinkyOption;
chrome/linky.jar:context/select-links.js
Line 407
from:
const linkySelect = new LinkySelect;
to:
var linkySelect = new LinkySelect;
chrome/linky.jar:context/shared.js
Line 44
from:
const linkyShared = new LinkyShared;
to:
var linkyShared = new LinkyShared;