Update 20.0.1 Rated 5 out of 5 stars
Same issue, choices disappear from Add-On bar, but still available in menu and context menu.This review is for a previous version of the add-on (0.92.00.1-signed.1-signed).
As I wrote in version information I removed the code to show it by the options panel.
You can move the button in the addon bar by using the standard customize of firefox.
Thanks for your report.