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!

Thanks Tylerdowner that seems to have done the trick.

Three weeks later and the problem has reoccured with a much longer video. I am not understanding why this is happening. If I did I might be able to prevent it. This is happening on both my computers now. Any suggestions would be welcome. Michele

Did you try to clear the cache?

• Tools > Options > Advanced > Network > Cached Web Content: "Clear Now"

Did you download the video that you hear with an extension or was this only a web page that you've visited?

It is possible that there is a problem with the files sessionstore.js and sessionstore.bak in the Firefox Profile Folder.

Delete the sessionstore.js file and possible sessionstore-##.js files with a number and sessionstore.bak in the Firefox Profile Folder.

• Help > Troubleshooting Information > Profile Directory: Open Containing Folder
• http://kb.mozillazine.org/Profile_folder_-_Firefox

Deleting sessionstore.js will cause App Tabs and Tab Groups and open and closed (undo) tabs to get lost, so you will have to create them again (make a note or bookmark them).

• http://kb.mozillazine.org/Multiple_profile_files_created

I will investigate your suggestions. I have not downloaded these videos just watched them online... I have also cleared my cache as suggested but that did not solve the problem. I am wondering whether there is something going on between youtube, firefox and Skype. I conference on Skype at times when watching these videos with other people.

Removing the sessionstore files has fixed the problem temporarily but I wonder what will happen next time I watch a video and use Skype at the same time. Thanks for your help Cor-el. Michele

Follow up information. Although removing sessionstore files yesterday solved the problem on the day, this morning I start Firefox up and the soundtrack has returned. So short of clearing session stores everyday this is not going to be the solution. I appreciate the help you have given me but obviously there is a root problem that has yet to be found and solved. Michele

Which security software (firewall, anti-virus) do you have?

Some security software has virtualization or sandbox features that may cause problems by protecting and restoring files in the Firefox profile folder.

There are way to show the links in a sessionstore.js file.
Maybe you can use them to see if you can identify the cause.

See this MozillaZine forum thread.

• http://forums.mozillazine.org/viewtopic.php?f=38&t=622036&start=60&p=12098147#p12098147
• http://forums.mozillazine.org/viewtopic.php?f=38&t=622036&start=45&p=10768811#p10768811

I'll have a look at your suggestions. I use Norton 360 as my security software. Thanks for the info I will come back when I have digested and carried out any action necessary.

This problem just started for me. I've cleared cache/history,etc. A Youtube video I watched a few days ago keeps randomly playing in the background. Nothing on the screen, just the audio track.

The reset will probably clear it from what I've read but does not prevent it or explain it...seems like swatting a gnat with a sledge hammer to me.

Jahfre, you are right clearing cache etc and resetting does not stop it from happening again. I have two PC and it is now happening on both. I daily remove the sessionstore-##.js file as Core-el posted above and that solves the problem for the day but when I boot up the next day it starts up again. I have not had time to go through the forum links to see if I can find a solution there. It will have to wait til I have more time. Good luck and post back if you find a solution. thx

You should never see numbered sessionstore-##.js files in the Firefox Profile Folder.
The presence of such files always indicate that the original sessionstore.js was locked by other security software (firewall, anti-virus) and that Firefox wasn't able to replace the file with a new copy.
You will have to check the setting in your security software and exclude that file or the Firefox Profile Folder from that scanning/locking.

I found the offending link in a file called prefs.js

I only have one sessionstore.js file. It doesn't appear to be related to my problem.