Video format or MIME type is not supported error in Firefox

Matthew Adams
by Matthew Adams
Windows & Software Expert
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  • Playback errors in Firefox could happen if the file type is not supported. 
  • In this article, we take a look at different ways to deal with this issue. Continue reading for more.
  • For other issues, please check out the Firefox errors section on the site. 
  • Comprehensive guides about this browser are found in the Firefox Hub
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Are you getting a MIME type not supported error or video format error when attempting to play videos on websites open in Firefox?

When that happens, the videos display this error message, Video format or MIME type is not supported. Consequently, the video doesn’t play in the browser. One Firefox user stated:

When attempting to watch any program on there is an error message across the screen where I would normally see the program. ‘Video format or MIME type is not supported,’ I have never had this before with Windows XP or Windows 10.

Mozilla, and other browser developers, have ditched plug-ins in favor of HTML5. As such, Firefox no longer supports most plug-ins. The one exception is Adobe Flash as Flash videos are still prevalent.

However, there are still quite a few websites that include media content that depend on antiquated plug-ins.

Consequently, videos on sites that haven’t been updated are returning MIME type errors. Here are a few potential fixes for the MIME type Firefox error.

How can I fix the unsupported video format error in Firefox?

1. Switch to Opera

If the video format errors persist in Firefox, consider making the switch to Opera.

You must know that you will not be missing out on any features that you already like. Video pop-out is available in Opera as well. It was actually first introduced here and then other browsers copied it.

Support for extensions is also present and Dark Mode or Built-in Snapshot are also available.

You will, however, get a number of extra functionalities such as:

  • Free, unlimited VPN
  • Built-in messengers
  • Unit converters
  • Crypto Wallet

and a lot more. You can see what else is included by clicking the Learn More button below.



Make the switch and see the improvements. MIME types can be edited for improved support

2. Add the latest Flash plug-in to Firefox

As Firefox still supports Adobe Flash, make sure the browser has the most updated version of that plug-in. The plug-in usually has automatic updates, but you can ensure that Firefox has the most updated Flash version by pressing the Install Now button on this web page.

  1. Deselect the optional offers checkboxes so that extra software isn’t installed.
  2. Press the Save file button to save the Flash installer.
  3. Then press the arrow button on Firefox‘s toolbar (or Ctrl + J), and click the Flash installer to open the Adobe Flash Player Installer window.
  4. Press the Finish button after installation.
  5. Restart the Firefox browser.

Want to unblock Adobe Flash content in Firefox? Follow the simple steps from this guide.

3. Clear Firefox’s Cache

  1. First, click the Open menu button at the top right of Firefox.
  2. Select Options to open the Options tab.
  3. Click Advanced > Network to open the settings shown directly below.
  4. Press Clear Now to the clear the cache.

A corrupted cache can generate website errors. So clearing Firefox‘s cache could feasibly fix the MIME type video error.

Need more info on how to clear Firefox‘s cache? Check out this handy article.

4. Clear Firefox’s Cookies

  1. Deleting corrupted cookies might also resolve the MIME type error. To do that, open the Options tab in Firefox again.
  2. Select Privacy and select Use custom settings for history from the drop-down menu.
  3. Then you can press Show Cookies to open the window directly below.
  4. Press the Remove All button to erase the cookies.

Performing these operations is safe, but a bit time-consuming.

Since there are best practices to keep your computer in shape and remove old files, junk, cookies, and cache, you should get CCleaner.



Speed up your computer. Perform cache cleanup and delete cookies from Firefox and others with the world's #1 PC Cleaner.

5. Install the Media Feature Pack on KN and N Windows editions

Not all Windows editions include the media-related technologies Firefox needs to play media content.

Windows KN and N editions don’t include Windows Media Player, WMP Active X, the Windows Media Device Manager, Windows Media Format and are also missing a few audio codecs.

As such, missing media technologies can also be a factor behind video and audio playback errors in Firefox for Windows KN and N users.

Installing the Media Feature Pack will restore many of the missing media features in KN and N editions. There are three Media Feature Packs for different versions of Windows 10 KN and N.

You can download the packs from any of the three pages below. Install the Media Feature Pack that best matches your Windows 10 version.

Add the NoPlugin extension to Firefox

If the MIME type error still isn’t fixed, check out the NoPlugin add-on for Firefox. This add-on scans website media content for plug-ins and converts the plug-in code to HTML5 players so that you can play the video in browser.

If the browser still can’t play the media content, NoPlugin downloads the video so that you can play it in a media player. You can add NoPlugin to Firefox by pressing the + Add to Firefox button on this website page.

With the add-on installed, open the web page that includes the video displaying the MIME type error message. Now the video might work in Firefox.

If the video still doesn’t play, press the Open content button to download the media content. Then you can play the video in a media player that supports the video format.

If the videos still aren’t playing in Firefox with the NoPlugin add-on, you may need to update the browser to a version that more fully supports HTML5.

You can update Firefox by clicking the Open menu button > Open Help Menu > About Firefox. That will open the window below from which you can press a Restart Firefox to Update button.

update firefox

Those are a few fixes for the MIME type not supported error that will restore video playback in Firefox. As the web continues to embrace HTML5, more and more sites will become HTML5 compatible.

That will reduce plug-in video errors, but for now, the NoPlugin add-on is a good remedy for websites that still rely on outmoded plug-ins.

If you have any other questions, don’t hesitate to leave them in the comments section below.

Editor’s Note: This post was originally published in July 2017 and has been since revamped and updated in July 2020 for freshness, accuracy, and comprehensiveness.