Fix https://github.com/danbooru/danbooru/issues/4783#issuecomment-912426739: Spoke too soon. It works in flash posts, but not in non-flash posts. Here's the full trace that happens by trying the Shift-E shortcut (tested on https://danbooru.donmai.us/posts/4749304 with the latest ruffle for chrome at https://ruffle.rs/#downloads): 4749304:7 Uncaught TypeError: Cannot read properties of undefined (reading 'appendChild') at Object.initialize_ruffle_player (application-237cebbe071cb34ce095.js:1) at Object.initialize_all (application-237cebbe071cb34ce095.js:1) at HTMLDocument.<anonymous> (application-237cebbe071cb34ce095.js:1) at f (857-ff5115a2d6ceb23b4291.js:2) at p (857-ff5115a2d6ceb23b4291.js:2) at nrWrapper (4749304?q=status%3Aany:7) Caused by trying to initialize the Ruffle player on non-Flash posts, because we checked for the existence of the `window.RufflePlayer` object to tell if we were on a Flash post, but when using the Ruffle browser extension the RufflePlayer object will always exist.