On Windows XP, Firefox does not have the necessary code to play MP4s itself, a plugin is needed. What happens if you try to load that MP4 directly -- does a plugin handle it? https://video.twimg.com/ext_tw_video/717551104695742465/pu/vid/1152x720/5AhNwpuasEYxhKFu.mp4

Since Twitter does not "fail over" to Flash or another plugin gracefully, you need to use a workaround to play the media using either QuickTime or VLC (or another plugin that can handle MP4 video).

In the other thread, I linked to my user script to detect the failure message and display link to open the video "stand alone" in a new tab to be played using QuickTime. There are two steps for using this workaround:

(1) First, you need the Greasemonkey extension:

https://addons.mozilla.org/firefox/addon/greasemonkey/

(2) Second, install the script from here:

https://greasyfork.org/en/scripts/12427-twitter-html5-video-error-to-link

With that installed, you could expect to see something like the attached screen shot when you try to play a video on Twitter.

Does that work for you?

That script won't work on Streamable because the video fails silently behind the "poster" image, and the script is keying off Twitter's error message. (Example: https://streamable.com/s/nba) If no one has built a general solution yet, I'll look for a different way.

To download either of those players/plugins:

• VLC from VideoLAN:
  http://www.videolan.org/vlc/

• Apple QuickTime for Windows:
  http://www.apple.com/quicktime/download/
  Note: you can uncheck the box and skip giving them your email address and go straight to the download.

The Greasemonkey Script no longer works. I think it now bypasses it.

I can only test by disabling the Windows Media Foundation in my Firefox on Windows 7 (switch media.wmf.enabled to false in about:config). Then I get the display shown in my earlier screen shot.

Can you check your Add-ons page to make sure that your MP4-playing plugin is enabled? Either:

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

In the left column, click Plugins. On the right, look for QuickTime or VLC, whichever one you chose to install, possibly toward the bottom, and make sure its permission is the default of "Ask to Activate" rather than "Never Activate". Usually that change takes effect immediately, but in some cases you might need to test in a new window or after exiting Firefox and starting it back up again.

I do not have VLC or Quicktime on my plugins list. I do have VLC installed, but it is not my default program. I have no default programs as a matter of fact, though one I do use the most is Media Player Classic.

I also switched the WMF toggle to false, just to see if anything changed. It didn't work.

Hmm, if you have the main VLC app, I think that should have installed the plugin, too. You do not need VLC to be your default media player on Windows in order to use the plugin in Firefox. If it's there!

If you want to try the Microsoft plugin -- I can't recall testing whether it can play MP4s -- check out this article: Play Windows Media files in Firefox with the Windows Media plugin (two steps: install and configure).

Anyway, you need at least one plugin that can MP4s to resolve this issue on Windows XP.

(Windows XP doesn't have Media Foundation, so the wmf preference doesn't do anything on XP, either way.)

There was no way to get the plugin detected inside Firefox, so I was forced to uninstall and reinstall VLC completely. But now it works again.

I'll keep this thread open for when I have a Vine or Streamable issue.

Here's a new problem: this time, unrelated to Twitter applications. This is with Daily Motion. Simply put, I can't play most videos there. Some videos will play, other videos will not. It's a crap shoot situation.

For example, I can play this video: http://www.dailymotion.com/video/xpk3k2_g255-ill-met-by-moonlight_shortfilms

But I can't seem to play this video: http://www.dailymotion.com/video/x5r0je_weird-al-on-family-double-dare-part_fun

The screenshot below shows what it looks like when the video refuses to play. Endless ellipses.

The Greasemonkey script for playing videos on Twitter has stopped working once again. Here is a sample tweet: https://twitter.com/Albeanu/status/730583808131534848

Oh boy, now they serve these M3U8 files instead of MP4 files. I can generate a link to the file, but I can't play it (Firefox shows a download dialog).

That file has individual M3U8 URLs for different resolutions. Then each resolution has a bunch of URLs with various numbers in the address that I suspect are time intervals, meaning, this 15 second clip needs 5 files to play:

#EXTM3U #EXT-X-VERSION:6 #EXT-X-MEDIA-SEQUENCE:0 #EXT-X-TARGETDURATION:4 #EXTINF:3.000, /ext_tw_video/730583207955992578/pu/vid/0/3000/640x360/RiWtJS497dP2Lz13.ts #EXTINF:3.000, /ext_tw_video/730583207955992578/pu/vid/3000/6000/640x360/Bm3vjJjFKsuMBU5z.ts #EXTINF:3.000, /ext_tw_video/730583207955992578/pu/vid/6000/9000/640x360/J8qBowzjQ0BgqL6i.ts #EXTINF:3.000, /ext_tw_video/730583207955992578/pu/vid/9000/12000/640x360/CQiHlrOckWjgOlq5.ts #EXTINF:3.078, /ext_tw_video/730583207955992578/pu/vid/12000/15078/640x360/rpu_jVLRHHJD2OV2.ts #EXT-X-ENDLIST

I have no idea how to fix this. I can't make VLC handle it. Frustrated after 2 hours of trying.

I added handling for https://mobile.twitter.com/ which might be the last hope.

I have this same problem. Windows XP. I know, it's a dinosaur.