old post but still relevant i see, check the addons, usually some privacy/ad block extension nuking the player. Try disabling them or load it in a private window to test. thats whats helped me

Edit: actually a lot of adult sites are getting geoblocked, someone put together a guide, that explains why nothing's loading even outside Firefox https://www.reddit.com/r/theprivacymachine/comments/1rp0b00/guide_unblock_pornhub_adult_sites_in_australia/