Рейтинг 4 из 5 звёзд

Extremely useful and helpful! Almost 5 stars except that it is difficult to set options to launch links between Thunderbird and two Firefox profiles. Frequently get "Thunderbird|Firefox is already running" error. Sometimes links clicked from Thunderbird open in non-default Firefox profile.

(MOZ_NO_REMOTE and new_instance options need to be documented better).

Это отзыв для предыдущей версии этого дополнения (1.7.6.1). 

Unfortunately there isn't a perfect solution for that problem, it's a limit of Firefox/Thunderbird core code. If you're not on Windows, the better option is to use "new_instance"; if you're on Windows, try to reset "MOZ_NO_REMOTE" at startup.