Sometimes, the video or audio content in a web page cannot be properly downloaded and displayed in Firefox. This article will help you solve these problems. Note: If you're having trouble with a website, click the icon in the address bar to see if Firefox has blocked parts of the page that are not secure. See Mixed content blocking in Firefox for details. Firefox may be blocking media with sound from playing automatically. To allow media autoplay, see Allow or block media autoplay in Firefox. HTML5 audio and video Firefox has built in support for open media formats usually associated with MP3, WebM, Ogg and Wave containers. However, MP4 containers usually depend on platform decoders for AAC and H.264 audio and video streams. For more information, see Fix video and audio playback problems on Firefox for Windows and HTML5 audio and video in Firefox. Or Some versions of Windows are missing Windows Media Player and other media-related technologies needed to decode and play videos and music properly. Microsoft offers a Windows Media Feature Pack (for versions designated as Windows N and KN editions) and a Platform Update Supplement (for Windows Vista and Server 2008) that you can download to add this functionality. Here are some problems that people have reported when the Windows Media Feature Pack is missing: "Why is YouTube video blurry, low resolution, or black?" "Why do I get Flash instead of HTML video?" "Why doesn't Vimeo work?" "Why do I get a Netflix error that Microsoft Silverlight is required?" Solution To resolve this, please download and install the Media Feature Pack or Platform Update Supplement that's appropriate for your version of Windows. Visit Microsoft's support article to find your version of Windows. If you update Windows to a newer version, for example, from Windows 10 Version 1803 to Windows 10 Version 1809, you'll need to redownload and install the Media Feature Pack even though you installed it for the previous Windows version.