Hello,

This is a Firefox bug - every add-on that you pin will disappear after it's upgrade. And since I'm actively developing my add-on, there is a lot of disappearing (I've released new version even today).
I could program a work-around that would store the position of pinned tabs and then restore them after the upgrade, but it's not easy and there is just no time for that right now (I'm really sorry, but as a full-time addon developer my income is now extremely low and I need to focus on things that maters...).

Have a nice day :)

Best regards,
Juraj Mäsiar