I don't see why this would stop working. Could you try the support process for the add-on? http://www.downloadhelper.net/support-expert.php

Also, the current release of Firefox is Firefox 27. When you're ready to upgrade, you can use Help > About Firefox > Check for Updates.

The download helper support only recommended I use the most recent version and I already was. Any other suggestions?

I am now using v. 27 with the same result.

As jscher2000 mentioned, this shouldn't happen at all since you have no other extensions installed that would interfere with it. You might want to try contacting the developer. http://www.downloadhelper.net/contact-us.php

This is so frustrating. I am using the newest version Fire Fox and Download helper. The You Tube video starts to download but quickly goes to a failed conversion. Does anyone have any new ideas?

What error message does it give?

I've used the extension, but not the conversion feature. Maybe update the ConvertHelper? http://www.downloadhelper.net/conversion-manual.php

I updated and tried the ConvertHelper...still doesn't work.

The message I get is:

Conversion job completed 'filename'.wmv failed converting

Could there be a problem with my converter license even though nothing indicated there is?

I tried the online helper and it was no help.

I don't have any other ideas, sorry.