Your More System Details indicates that the primary method Firefox uses to play MPEG encoded media on newer versions of Windows is blocked. Maybe that is causing the mis-handling.

Try this:

(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 filter box, type or paste media. and pause while the list is filtered

(3) Double-click media.windows-media-foundation.enabled to switch its value from false back to true (the default value).

This could have been disabled to allow easier downloading?

With the last Firefox upgrade, some plugins are no longer enabled until you enable it.

Open the Add-ons Manager. Press the <Alt> or <F10> key to bring up the tool bar. Followed by;

Windows; Tools Linux; Edit Mac; application name

Then Add-ons.

Hot key; <Control> (Mac: <Command>) <Shift> A)

On the left side of the page, select Plugins.

BTW; At the top right is a link to check your plugins.

@jscher2000

I switched it to true but im still getting the same error.

@FredMcD I don't want to enable a plugin though.

Could you link to a page that has the problem?

Also, in case it's not an MPEG-related issue, could you test a WebM video to make sure it plays without a plugin: http://www.webmfiles.org/demo-files/

This video will not load. http://channel9.msdn.com/Series/C-Sharp-Fundamentals-Development-for-Absolute-Beginners/Series-Introduction-01

along with this http://www.gfycat.com/RemorsefulShyBlueandgoldmackaw

(random examples)

the WebM video loaded fine

The Microsoft page has a preference for MP4 and the other page has a preference for WebM. If you click the links to the videos, will they play stand-alone in a tab? If so, and you right-click, do you get a Firefox context menu or a plugin-specific context menu?

<video>
 <source src="http://media.ch9.ms/ch9/00c3/9fbe89f0-7db8-422f-937a-3fff81e100c3/Series-Introduction-01_mid.mp4" 
  type="video/mp4">
 <source src="http://media.ch9.ms/ch9/00c3/9fbe89f0-7db8-422f-937a-3fff81e100c3/Series-Introduction-01.webm" 
  type="video/webm">
</video>

<video>
 <source src="//zippy.gfycat.com/RemorsefulShyBlueandgoldmackaw.webm" 
  type="video/webm">
<source src="//fat.gfycat.com/RemorsefulShyBlueandgoldmackaw.mp4" 
  type="video/mp4">
  Sorry, you don't have HTML5 video and we didn't catch this properly in javascript. You can try to view the gif directly: <a href="http://giant.gfycat.com/RemorsefulShyBlueandgoldmackaw.gif">http://giant.gfycat.com/RemorsefulShyBlueandgoldmackaw.gif</a>.
</video>

Also, could you test with the DivX extension disabled? You can do that on the Add-ons page. Either:

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

In the left column, click Extensions, then you can disable extensions on the right side.

The links work now but what can I do to fix it?

I have DivX extension disabled already.

There are other things that need your attention.

Your System Details list shows that you have a user.js file in the profile folder to initialize prefs each time Firefox starts.

The user.js file is only present if you or other software has created this file and normally it wouldn't be there. You can check its content with a plain text editor (right-click: Open with) if you didn't create this file yourself.

The user.js file is read each time Firefox is started and initializes preferences to the value specified in this file, so preferences set via user.js can only be changed temporarily for the current session.

Delete a possible user.js file and numbered prefs-##.js files and rename (or delete) the prefs.js file to reset all prefs to the default value including prefs set via user.js and prefs that are no longer supported in the current Firefox release.

You can use this button to go to the currently used Firefox profile folder:

• Help > Troubleshooting Information > Profile Directory: Show Folder (Linux: Open Directory; Mac: Show in Finder)

See also:

• http://kb.mozillazine.org/Preferences_not_saved

@ cor-el @ jscher2000

THANKS SO MUCH! It works now; I had to disable divx in the extensions label not add-ons.