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.

What version of Download Helper do you have? You can search for it on this page

Help > Troubleshooting Information

and then compare with this page

https://addons.mozilla.org/en-US/firefox/addon/video-downloadhelper/

Note: If the Troubleshooting page shows "false" in the Enabled column, you need to enable the extension here:

Tools > Add-ons > in the left column, click Extensions

Does that help?

You can check for problems caused by a corrupted localstore.rdf file if you can't find the downloadhelper toolbar button on the Navigation Toolbar or in the toolbar palette.

• View > Toolbars > Customize

• http://kb.mozillazine.org/Corrupt_localstore.rdf