Rated 4 out of 5 stars

Working well on 68.2.2. My Linux distro had v60 and baked in lightning. I had to uninstall all mozilla, reinstall FF and TB from the web, delete .local TB folder, and then install cal provider from add-ons, bypassing my distros repo. No issues now.

This review is for a previous version of the add-on (68.2.1).