Sorry for replying so late.
Add-on are does not work in some of the specific page.(eg "about:blank", , "about:home", "addons.mozilla.org" ...)
Also this add-on does not work when prevent touch event by javascript of the page you are viewing.
As other causes, this add-on may have a bug... (Sorry, I will not be able to fix it soon.)
thanks.

2019/02/28
I could confirm it with my smartphone.
However, I will not be able to fix it soon...
(It may be a bug in the Webextensions API)

2019/02/28 - 2
When the view is zoomed in, javascript seems to get the wrong touch position and scroll position.
Please wait for firefox is fixed.