Developer of one of the extensions said it like that and I don't know what they meant. Here: https://dev.fandom.com/wiki/Talk:Tooltips#Untitled
As for me, I have 4 extensions present on the wiki. ImportJS looks like this:
dev:UserFunctions.js
dev:Tooltips.js
dev:ReferencePopups/code.js
dev:ReferencePopups/custom.js
But only ReferencePopups seem to work.
It also has a weird bug: Tooltips extension works but only on the first page after refreshing Fandomdesktop.css ONCE. Refreshing the page again or going on any other page will result in the script not working again.