It seems that other Mozilla apps don't play well with WB, either. Firefox doesn't skin properly and has to be excluded for it to appear correctly in default settings. However, Thunderbird has another issue that prompted me to discontinue using it. It was sending 2 to 3 copies of every email I sent, sometimes more. At one point it sent 6 copies of a particular email, which prompted an me to switch to Win 10's built-in email app after I got an angered response from the recipient.
