I was able to apply the patch to the network.js file in
/usr/share/webext/eas4tbs...@jobisoft.de.xpi and now it works as expected.
- Bug#1038628: webext-eas4tbsync: MS Exchange OAUTH2 setup fail... Paolo Miotto
- Bug#1038628: Acknowledgement (webext-eas4tbsync: MS Exch... Paolo Miotto