Am I being stupid?
I can't find any link of plugins in this website.
I can do nothing because there is no appropriate plugin/behavior/effects...
Develop games in your browser. Powerful, performant & highly capable.
Try searching for the same topics in google and open cached results. If google cached the old page (on scirra.com), you will be able to see the download links.
Also, you can browse some posts from 2016 saved on web.archive:
web.archive.org/web/20160519014331/https://www.scirra.com/forum/completed-addons_f153
.
Tom from Scirra is working on restoring the links in posts, he assured that they are not lost and will be recovered soon.