I'm having a problem with embedded content being displayed in-frame such as tweets and media previews. I'm pretty sure it's caused by one of the settings I've added to about:config/prefs.js but I'm not sure which one and I've been trying to figure it out for weeks. I've attached an image showing what I see instead of media previews. Can someone help me identify which line in prefs.js is causing this to be blocked? Also one other short unrelated question. I've noticed that some of my preferences get moved or copied to another file that firefox spawns called InvalidPrefs.js Does this mean those prefs are outdated and do not work anymore?