Loads all manga pages at once in a simplified vertical layout
Clicking on each image scrolls down to the next image. This seems to work as it always has for both multi-image illustrations and manga, in both Greasemonkey 3.17 and Violentmonkey 2.9.9, on both Firefox ESR 52 and Basilisk 2018.09.
This script never implemented keyboard controls, so I'm not clear on what broke.
scroll for manga became broken with pixiv update
Pixiv made new viewer for manga that uses onscreen arrows for flipping pages, even though the script still presents all images on one page vertically, there's no way to scroll the page any more. Multi image illustrations still use old layout, which is unaffected.