Firefox downloads

Hi guys,
I'm using Firefox's Video DownloadHelper to get some streaming videos and I realised that it actually creates two files, a .mp4 and a .part file in the folder while it's downloading. So I am unable to track the folder and just watch for .mp4 files.
I'm thinking a way could be to check for duplicate filenames, so when the .part file completes and disappears, and only a single .mp4 filename is there, then an action can be issued. But I've no idea how to do that.
Or is there a better way to wait to apply the action only when the download completes?
I've searched the forum and found the old thread about Firefox where someone asked about the PDF download, but I think the solution doesn't seem to be applicable here? Like checking date modified (it doesn't seem to change until download completes) or waiting for a few minutes as the download ranges from few minutes to few hours, so can't really have an accurate gague for that.
Thanks in advance!
I'm using Firefox's Video DownloadHelper to get some streaming videos and I realised that it actually creates two files, a .mp4 and a .part file in the folder while it's downloading. So I am unable to track the folder and just watch for .mp4 files.
I'm thinking a way could be to check for duplicate filenames, so when the .part file completes and disappears, and only a single .mp4 filename is there, then an action can be issued. But I've no idea how to do that.
Or is there a better way to wait to apply the action only when the download completes?
I've searched the forum and found the old thread about Firefox where someone asked about the PDF download, but I think the solution doesn't seem to be applicable here? Like checking date modified (it doesn't seem to change until download completes) or waiting for a few minutes as the download ranges from few minutes to few hours, so can't really have an accurate gague for that.
Thanks in advance!