today at startup my Tb (not precisely sure what version it was) asked if it should check compatibility of the lightning calendar addon. That is to say it displayed in a list windows the only item: lightning and said it was not compatible. Choices were "check" or "don't" check compatibility. I clicked on check and after nothing happened for several minutes on "cancel". So, now my Tb is upgraded to 15.0 and Lightning isn't there anymore. It never asked me to upgrade anyway and I urgently need my calendar now.
Any suggestions warmly welcome!
Edit: Solved!I had to reinstall lightning and provider for google calendar addons - although they were already installed and obviously falsely not found compatible.
The question now is how to avoid automatic updates in tb in general...