Hello, I only figured it out today as I don't visit Facebook often. I don't have Facebook APP in my cell phone, as I don't want to. I only visit it when using notebook which has WIndows 10 and Firefox. It seems that the autoplay blocking configuration of Firefox is not working on Facebook Messenger web version. Videos keep autoplaying in a conversation, even though we don't want it and have it configured both in Firefox and even Facebook to be blocked. So, resuming, autoplay blocking doesn't work even though is selected in Firefox and Facebook. It happens the same in Edge. They might be using a different way to avoid the blocking definitions, both from Facebook and Firefox In Messenger Lite in Android and Messenger for Win10, autoplay blocking works fine. I reported to Facebook but I don't expect any answer from them as usual. If you could help it would be great. Thanks in advance.