Version 1.2.13 worked OK on Thunderbird 52.9.1 (32-bit, but it's running on a 64-bit machine.) today. Immediately after decoding our TNEF document, TBird updated itself to 60.3.0 (still 32-bit) and disabled LookOut. Bummer.
I installed this to try to open a mail with a winmail.dat file attached. After restarting thunderbird after installing the add-on, the mail wasn't there anymore. Disabled the add-on, the mail isn't coming back.
Works fine with TB 38.3.0 under Windows 10! For those who might still have problems with winmail.dat, LookOut is not compatible with the addon "Thunderbird Conversations". The solution is to open the mail in a new tab (right-clic on the email). This way, Thunderbird uses the old template to display the message and winmail.dat is decomposed. Attachments can now be open... Again, thank you Micro$oft for your great work! :-(