I have now migrated our site to a new theme unconnected to the old one. The issue with the slide function is still present with the new theme, again only on mobile Firefox.
Since I tried (in the old theme) with all other plugins disabled, the fact that it is still the same in a completely new theme suggests that the issue is with your plugin, and not a result of a conflict with the theme or other plugins.
I really like the functionality of your plugin and the control it gives me. I hope you can resolve this soon.