Comment # 45 on bug 1084603 from Wolfgang Rosenauer

I still have a bit of the suspicion that it might be related to the crypto
library NSS.
Stock Thunderbird comes with a quite old one and on openSUSE we use a much more
recent one to satisfy Firefox dependencies. I would not expect such an issue
resulting from that because that library is meant to be mainly ABI compatible.
As upstream is just about to release version 60 of Thunderbird my hope is that
this issue goes away with that version to match Firefox 60esr.

I should have first candidate packages for Thunderbird 60 within the next week
or so to see how it behaves.