Try the following, I have tried and it works. The loading bar is back! '''Clearing the cache''': Tools > Options > Advanced > Network > "Clear now" [button]. And: '''Deleting cookies related to YouTube''': Tools > Options > Privacy > History > Firefox will: [select] "Use custom settings for history" [from drop-down] > "Show cookies" [select and follow the steps below] For deleting cookies, using the search bar, search for "youtube" and delete all the cookies related to it. After everything, reload your youtube link. Hope it works ! =)