butterflying_low, what are your current autoplay settings? To check your autoplay settings you can do the following: # go to the Tools menu (alt+T) and select settings. # in the settings page, search for "Autoplay". # find the Autoplay section in the results and press its settings button. Assuming that you want autoplay enabled, then you can do the following. But first you may wish to note down the existing settings before making any changes, so that you can restore them if the following doesn't make things work the way that you want. Also, remember to press "Save Changes" and you may need to restart Firefox for the changes to take effect. If the "Default for all web sites" setting is set to something other than "Allow Audio and Video", then try changing it to this. Or if there is a Youtube exception listed with a setting that is something other than "Allow Audio and Video", then try either removing this exception, or changing it to this.