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In TB 17 in 64bit Linux, the add-on correctly blanks out the From account. But as soon as you start typing in the body of the message, the focus changes to the From field, and a "random" account appears. Maybe it's using type-ahead because the focus changed, but that's not how I expected the add-on to work. Oh well, at least the From account is blank, which catches my eye enough to cause me to select the right account.

Это отзыв для предыдущей версии этого дополнения (1.3.1). 

The behavior you're describing is by design.
When no "From" account is selected the addon won't let you start writing your mail. Instead it'll focus the "From" account dropdown.
What you're experiencing as "random" account is caused by the typing of letters with the dropdown active.