Join the AMA (Ask Me Anything) with the Firefox leadership team to celebrate Firefox 20th anniversary and discuss Firefox’s future on Mozilla Connect. Mark your calendar on Thursday, November 14, 18:00 - 20:00 UTC!

This site will have limited functionality while we undergo maintenance to improve your experience. If an article doesn't solve your issue and you want to ask a question, we have our support community waiting to help you at @FirefoxSupport on Twitter and/r/firefox on Reddit.

Search Support

Avoid support scams. We will never ask you to call or text a phone number or share personal information. Please report suspicious activity using the “Report Abuse” option.

Learn More

Videos no longer streaming

  • 5 iimpendulo
  • 1 inayo le ngxaki
  • 16 views
  • Impendulo yokugqibela ngu Mugsy

more options

Something changed and I don't know what.

For some reason, I suddenly can't watch mp4 videos as they download.

I checked my Options | Applications for MP4 files and the default was changed to Quicktime (but I did not install or update anything from Apple.) I don't remember what my previous plugin was (it was connected to the "MPC Media Player" package), but it definitely wasn't QT or WMP.

QT has a documented problem streaming video within Firefox. Setting WMP as the default player likewise tries to download the entire file before playing. I have tried adjusting the streaming settings of both players, but nothing I do makes a difference.

I have a fast 5Mbps DSL connection. The problem is not my player or connection. It's the plug-in associated with MP4 (others?) files.

How do I fix this? Thx.

Something changed and I don't know what. For some reason, I suddenly can't watch mp4 videos as they download. I checked my Options | Applications for MP4 files and the default was changed to Quicktime (but I did not install or update anything from Apple.) I don't remember what my previous plugin was (it was connected to the "MPC Media Player" package), but it definitely wasn't QT or WMP. QT has a documented problem streaming video within Firefox. Setting WMP as the default player likewise tries to download the entire file before playing. I have tried adjusting the streaming settings of both players, but nothing I do makes a difference. I have a fast 5Mbps DSL connection. The problem is not my player or connection. It's the plug-in associated with MP4 (others?) files. How do I fix this? Thx.

All Replies (5)

more options

Many site issues can be caused by corrupt cookies or cache.

  • Clear the Cache and
  • Remove Cookies
    Warning ! ! This will log you out of sites you're logged in to.

Type about:preferences<Enter> in the address bar.

  • Cookies; Select Privacy. Under History, select Firefox will Use Custom Settings. Press the button on the right side called Show Cookies. Use the search bar to look for the site. Note; There may be more than one entry. Remove All of them.
  • Cache; Select Advanced > Network. Across from Cached Web Content, Press Clear Now.

If there is still a problem, Start Firefox in Safe Mode {web link} While you are in safe mode;

Type about:preferences#advanced<Enter> in the address bar.

Under Advanced, Select General. Look for and turn off Use Hardware Acceleration.

Poke around safe web sites. Are there any problems?

Then restart.

more options

If you ope a file in an external program (media player) then Firefox will always download the full file before passing it to the player unless the file is a playlist file and not the actual media file. To play the file within Firefox you would have to have a plugin that supports the MIME type or file extension.

Firefox can also use the built-in HTML5 media player to play MP4 files provided that there is support on the OS level.


more options

Thanks for the replies.

I'm not sure why Firefox suddenly stopped playing MP4 files, and I wish I knew what app/plugin/etc was associated with mp4 files before. Now my only choices are WMP and Quicktime.

I tried reinstalling my preferred media player ("Media Player Classic") but it didn't help. Neither did reapplying my file associations from within the program (yes, I closed & reopened Firefox.)

I also tried toggling some obscure key in the "about:config" as recommended on Bugzilla, but it didn't help.

MSIE likewise also tries to download MP4 files rather than play them internally (not sure if this is new or not since I never use IE), so the problem almost certainly has nothing to do with cookies (and I use a ram cache.)

I'm running 64bit Win7. Firefox 34.0.5 (the latest version). I have no idea what program may have altered (I suspect) my MIME types.

Any ideas? Thx.

more options

Is Windows Media Foundation support enabled?

  • media.directshow.enabled = true
  • media.windows-media-foundation.enabled = true

Any error messages in the Web Console (Firefox/Tools > Web Developer)?

more options

Thanks for the reply cor-el.

"Yes" to both keys. "No" on error messages. :(