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When I click "install in Thunderbird" nothing happens
No error, but no add-on in the installed list as well

Это отзыв для предыдущей версии этого дополнения (3.5.1). 

That sounds like an addons site problem, but I can maybe help pin it down if you email me. Please raise issues via github, though, and not the ratings mechanism, I don't always see these.