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This is really a very useful addon. Unfortunately, it does not work anymore with Thunderbird 57.0b1. I had to start Thunderbird in safe-mode and deactivate it.

Это отзыв для предыдущей версии этого дополнения (4.7.1). 

Please check here:
https://www.mozdev.org/bugs/show_bug.cgi?id=26439

It's complicated but there are some explanations and a working test version available there.