YouTube is generally serving Firefox users an HTML5 player now instead of the classic Flash player. There may be a problem in your Firefox or your Windows with playing MP4 media without Flash.

First, you can check which player is not working by right-clicking the player and inspecting the bottom line of the short context menu. That typically will mention the specific plugin if a plugin is being used, for example, Flash or QuickTime. If that is not mentioned, most likely it is an HTML5 player.

Firefox can play OGG and WEBM videos natively without external assistance, but uses Windows Media Foundation to play MP4 video. There are some settings in Firefox to disable that; users who preferred to easily download MP3s sometimes changed those settings. Here's how you can check yours:

(1) In a new tab, type or paste about:config in the address bar and press Enter. Click the button promising to be careful.

(2) In the search box above the list, type or paste media and pause while the list is filtered

(3) {for Windows newer than XP} If the media.windows-media-foundation.enabled preference is bolded and user set to "false", double-click it to switch it to true

(4) {for Windows XP} If the media.directshow.enabled preference is bolded and user set to "false", double-click it to switch it to true

If you changed these settings, does that make any difference? I'm not sure whether the change takes effect immediately or after you exit Firefox and start it up again.

Users in Europe may need the Windows Media Feature Pack, but if your Windows came with Windows Media Player, then that probably does not apply to you. See:

• https://support.microsoft.com/en-us/kb/968211
• https://www.microsoft.com/en-us/download/details.aspx?id=16546

If this isn't fixed quickly, there is a quick and dirty workaround for YouTube, which is to use an add-on to force YouTube to give you the Flash player instead: https://addons.mozilla.org/firefox/addon/youtube-flash-video-player/

Umm, hold on, your "More System Details" does not show that you have a Flash player at all. So you may need to check that first.

Open the Add-ons page using either:

• Ctrl+Shift+a
• "3-bar" menu button (or Tools menu) > Add-ons

In the left column, click Plugins. Look for "Shockwave Flash" on the right side toward the bottom (grayed background area) and change it from "Never Activate" to "Ask to Activate".

(Note: When you visit a site that wants to use the Flash, you should see a notification icon in the address bar and one of the following: a link in a black rectangle in the page or an infobar sliding down between the toolbar area and the page. If you do not need Flash to run, maybe it's just an ad, you can ignore the notification.)

Sometimes plugin permission changes do not take effect for tabs in existing windows. You could test YouTube in a new window (Ctrl+n).

If Flash is completely missing from the Add-ons page: (or you need to update)

You can install Flash from this page, either the current 18.0.x series or the extended support 13.0.x series -- just choose the installer for "plugin-based browsers":

https://www.adobe.com/products/flashplayer/distribution3.html

You might need to close and re-open Firefox during installation (Adobe's installer will tell you if you need to do that).

Any improvement?

Actually, I followed the steps as you outlined in your first comment, and it worked immediately. I did have to restart firefox. I tried it first out of curiosity, but after I closed out and went right back in it worked immediately. Thank you so much for your help!

Hello,

I am glad to hear that your problem has been resolved. If you haven't already, please select the answer that solves the problem. This will help other users with similar problems find the solution more easily.

Thank you for contacting Mozilla Support.