Hello, Please try the reset firefox and visit the page to test if it was a saved preference. Otherwise please check the application saved settings as well as the http://contests.about.com/od/technicalassistance/ht/turnoffsounds.htm]

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 and some Preferences.

• Open websites will not be saved in Firefox versions lower than 25.

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!

Thank you.

You can check for issues caused by plugins.

• https://support.mozilla.org/kb/Troubleshooting+extension+and+themes

You can check for problems with current Shockwave Flash plugin versions and try this:

• check for updates for your graphics drive drivers
  https://support.mozilla.org/kb/upgrade-graphics-drivers-use-hardware-acceleration
• disable protected mode in the Flash plugin (Flash 11.3+ on Windows Vista and later)
• disable hardware acceleration in the Flash plugin

See also:

• http://kb.mozillazine.org/Flash#Troubleshooting

Note that you currently run Firefox in Private Browsing mode (browser.privatebrowsing.autostart: True)