I tried but Mediawiki:Common.js is read-only for me.
Oh, you're not an admin, so you can't edit Mediawiki pages. I've applied the script to the Etymology Scriptorium now. Hopefully there aren't many bugs...
Thank you very much! I just have created a test sub-page and it works fine. I have also posted a note in the Beer Parlour to invite others to try it.