Numerous times downloads will sale to 99% then stall for several minutes. This before Ff invokes anti-virus scan or Sandboxie prompts for recovery. It's not all downloads, just some. Is this Firefox or the download site or my ISP or Sandboxie?
Never happens to me. FF scans my downloads after it's completed downloading.
There my be a couple of reasons why this happens in some answers to the post you made about this over on Wilders forum