Please check if all your plugins are up-to-date. To do this, go to the Mozilla Plugin Check site.

Once you're there, the site will check if all your plugins have the latest versions. If you see plugins in the list that have a yellow Update button or a red Update now button, please update these immediately.

To do so, please click each red or yellow button. Then you should see a site that allows you to download the latest version. Double-click the downloaded file to start the installation and follow the steps mentioned in the installation procedure.

thaks, but it still doesn't work :(

Where are you trying to watch videos at? This thread is rather sparse on details.

on youtube

on youtube

The Reset Firefox feature can fix many issues by restoring Firefox to its factory default state while saving your essential information. Note: This will cause you to lose any Extensions, Open websites, and some Preferences.

To Reset Firefox do the following:

1. Go to Firefox > Help > Troubleshooting Information.
2. Click the "Reset Firefox" button.
3. Firefox will close and reset. After Firefox is done, it will show a window with the information that is imported. Click Finish.
4. Firefox will open with all factory defaults applied.

Further information can be found in the Refresh Firefox - reset add-ons and settings article.

Did this fix your problems? Please report back to us!

By all means try the Reset as advised by Tyler, but note you then loose extensions, open tabs, and possibly some settings, as explained in the article Tyler linked to. (You may wish to bookmark tabs, and extensions home pages. Plugins are not touched by reset)

I note you

• have been using the article Flash 11.3 doesn't load video in Firefox
• downgraded to Flash 10.3 (see system details aside)
• have RealPlayer related software/plugins, so please ensure that is all fully updated

If the reset does not work the next thing to try is disabling Flash Players protected mode, that solves a lot of FlashPLayer problems on Firefox Windows. (Not the simplest of tasks but this post contains links to instructions)

As an aside YouTube does or did have options to try HTML5 beta versions, you may need to check whether or not you are enrolled in that, as that may solve or cause problems in some circumstances.

it didn't fix my problem. when I want to watch any video I only see:

So what have you now tried

• The Firefox reset ?
• What plugins (Flash& RealPlayer related) and versions are now installed ?
• Have you turned off protected mode ?
  • What s the full text content of the file mms.cfg, please paste it in to the messsage
  • Check the file is actually mms.cfg, and not duplicated or accidentally named mms.cfg.txt , and that it is in the correct location.
• Are you able to watch any other Flash videos, or have you only tried the YouTube ones ?

I download and install Firefox anew, and now ( I dont know why) everything work!

Thanks for all your answers.

Glad you sorted it out, thanks for posting back.

We can not be sure what happened in your case, but it is pretty unusual for a simple uninstall and reinstall of Firefox to solve anything (because it tends by default to preserve the profile & extensions; and use the same plugins).