Do we agree the error message is always:
"[Exception... "The connection was established, but no data was ever
received" nsresult: "0x804b0014 (NS_ERROR_NET_RESET)" location: "JS
frame :: resource://gre/modules/DownloadCore.jsm :: this.DownloadError :: line 1498" data: no]"
This looks like a network error (like the connection between your computer and the server being temporarily broken). If there are sporadic connection problems, i presume you are more likely to get an error on a longer video than a short one.
There isn't much VDH can do here. The add-on's job is to detect video and initiates the download, but the download itself is performed by Firefox and VDH has no control on it (except for being notified once done).