Here are some easy-to-follow methods that can help you fix the youtube video error appeared in the Firefox issue.
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Why YouTube videos are not playing in Firefox?
Below are most of the reasons why videos won’t play on YouTube. One of the main reasons for this error is the corrupted history of your browser. If Firefox has an older cache and more advanced cookies, this can generally cause performance issues and other issues, including this one. So clear your cache with cookies to solve the problem.
Have you tried deleting the cookies and allowing youtube to load the page?
You may notice that the sqlite file that stores the cookies is corrupted if it costs a lot of money to delete the cookies.
Rename Cookies.sqlite (cookies.sqlite.old) (or Delete) removes cookies from other existing files, as with the cookie.sqlite-log file in a Firefox profile file if the file.sqlite cookie was passed in a corrupted .