Crashes or other problems with certain multimedia content in Firefox (such as YouTube videos and Flash animations or games) can often be resolved by performing the steps in these Knowledge Base articles:

• Flash Plugin - Keep it up to date and troubleshoot problems

• Adobe Flash plugin has crashed - Prevent it from happening again

Please tell us if this helped!

pieman2664 said

The most recent Firefox update was downloaded and installed a few days ago. Ever since when I try to watch YouTube videos, the video will just be black but the sound will be playing. It does this both on the YouTube website, and any other site that has shared a YouTube video (i.e. Facebook, Buzzfeed, news sources, etc;). I also updated flash player recently. I used internet explorer to see if it was my computer or just Firefox, and I was able to watch YouTube videos normally so it must be Firefox.

I have the same issue, videos on You Tube only play sound in Firefox, but the videos do play correctly in Chrome or Explorer. This seems to return after I have searched Firefox Help, found a solution, then upgrade to a 'new' Firefox version. The problem reoccurs.

Windows 7 Pro, Firefox 39.0

I did perform the following, per a Help suggestion:

"Tools > Options > Advanced > General > Browsing: "Use hardware acceleration when available"

But the "Use hardware accel. when available" was/is already selected.

Hi Paz 3, since the original time this thread was posted, YouTube started defaulting most Firefox users to an HTML5 players instead of a Flash-based player. If you right-click the video and check the last line on the short context menu, can you let us know which player is having the problem?

Regarding hardware acceleration, if it isn't working well you might need to update your graphics card/chipset driver software. Our support article recommends safe sites to do that: Upgrade your graphics drivers to use hardware acceleration and WebGL.

You also could consider testing in Firefox's Safe Mode. That's a standard diagnostic tool to deactivate extensions, hardware acceleration, and some advanced features of Firefox. More info: Diagnose Firefox issues using Troubleshoot Mode.

If Firefox is not running: Hold down the Shift key when starting Firefox.

If Firefox is running: You can restart Firefox in Safe Mode using either:

• "3-bar" menu button > "?" button > Restart with Add-ons Disabled
• Help menu > Restart with Add-ons Disabled

and OK the restart.

Both scenarios: A small dialog should appear. Click "Start in Safe Mode" (not Refresh).

Any improvement?