If I try to use ▼ and ▲ (▼ and ▲) for MediaWiki:Hidesection-show and -hide, the links don't work in Firefox. After clicking a hide link, for instance, the link is replaced with the entity text instead of the symbol, and the link doesn't work.
Pasting the rendered symbols instead of the HTML entities works fine.
Right, I understand.
I know what's happening here -- it's getting double-escaped. There will probably be something like data-hide="▼" in your HTML.
There's an obvious workaround. So what do you want me to do here? I guess I can unescape entities before having Mediawiki reescape here, but that seems like a kind of extra slowdown here.