I noticed that the script stopped working for all the dynamically loaded reply boxes: inbox replies, threaded replies and editing existing comments. I'm not sure why, but instead of XHR (which seems to be breaking fairly easily) it's now implemented as a DOM listener. Hopefully that's more robust and independent from the methodology AO3 uses to create the reply boxes.
In addition, the script now also works on /chapters/xxxx where you sometimes get directed instead of /works/xxxx