(In reply to Stefan Sitter [:ssitter] from comment #3) > You cannot install Lightning from xpi file anymore in Thunderbird 60 because > support for unpacked extension like Lightning was removed from the Mozilla > platform (Bug 1406499). To workaround and switch to the Lightning bundled > with Thunderbird see Bug 1454841 Comment 0 or Bug 1446537 Comment 5. See also this bug: https://bugzilla.mozilla.org/show_bug.cgi?id=1493008
Bug 1456577 Comment 11 Edit History
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(In reply to Stefan Sitter [:ssitter] from comment #3) > You cannot install Lightning from xpi file anymore in Thunderbird 60 because > support for unpacked extension like Lightning was removed from the Mozilla > platform (Bug 1406499). To workaround and switch to the Lightning bundled > with Thunderbird see Bug 1454841 Comment 0 or Bug 1446537 Comment 5. See also bug 1493008