You need to provide screenshot errors or site that is causing the issue for others to verify what is going on.

Hi Lizzie, if you check the download list (Ctrl+J), does Firefox say that those files are "moz-safe-about" files? Users sometimes get those on sites with certain kind of advertising -- for reasons that are not clear -- and they are empty (0 bytes). Being empty, I don't think those files are a concern, but they are annoying. To remove them, you can right-click one on the list and choose Delete.