hi apologies for the inconvenience but I can't support the older framework now as Firefox has mandated to migrate to newer WebExtensions.

You can still download the older version from https://addons.mozilla.org/firefox/downloads/file/420501/scroll_to_top-4.5.5-fx.xpi?src=version-history

You will have to disable automatic updates of the addon, its a simple setting on about:addons page.