You need to refresh the page (F5) to update the items in the download menu. Apparently YouTube refreshes the page in such a way that the extension doesn't gets notified, so you need to refresh the page manually if you want to download a media file from this page.

thank you for your reply.I'm a big fan of fire fox. Is there any possibility to solve this issue?unless we have to load the page twice.it is disadvantage for us.

I don't think that there is much that you can do about this apart from using the workaround to reload the page until this is fixed.

There is this bug about this issue:

• http://bugzilla.downloadhelper.net:8080/show_bug.cgi?id=642

I don't know if other download extensions suffer from this issue as well, so can try try a few more by searching the Add-on website and if possible use another format like WebM if available.

Also note that not all videos are downloaded and saved properly. Some can have a size of 0 bytes and fail to download, so best is the check in the Downloads Manager of toolbar drop-down list to make sure that the file size is correct (i.e. nor 0 bytes, but a more likely size).

YouTube continuously makes changes to the code and the way its web pages work, so extensions can fail at any time.