Rated 5 out of 5 stars
Sorry to see you won't upgrade it, although that's perfectly understandable. Mozilla is definitely at fault here and I dislike what they've been doing with Thunderbird lately, as many add-ons I've used for years stop working one after the other.
There's nothing special about v68 anyway, other than a broken dark theme (at least for me), so will stick to v60.
In any case thank you for your great work on this add-on!