''locking as a dupe of https://support.mozilla.org/en-US/questions/991198'' Searching support for two nights has led me to an answer because the help is almost always outdated. YouTube videos will not play using Firefox on my new desktop computer. I downloaded Flash player (version 12 something) using Firefox 28 after YouTube told me I needed it. After doing that, videos would play for a few seconds, then a message would appear telling the video would not play with a "Learn More" link. The help was too vague to help. I have Windows 7 Home Professional, security software, etc. If anyone is able to help, I am willing to provide more information about what I did and what kind of hardware and software I have. I have uninstalled Firefox and Flash plugin until I get a better handle of what I need to know to better troubleshoot this. YouTube videos will play when I use IE 11 without downloading a plugin. Oh, I see Mozilla has has guessed what kind of hardware and software I am using. They did a great job of doing so, but I am using my old laptop to make this post. I have never had problems with Firefox on this computer. Thanks you in advance.