Forum communautaire Firefox

After downloading a file which is saved to my Mac Download Folder the file is removed once I close the Firefox Web window. I checked the folder before the window was closed and the file was there. After closing the window the file is no longer in the folder. Also it is not in the trash.

I am trying to download videos from a site that I newly subscribed to. The videos do stream perfectly. The files do not download as video files and will not open at all. When I click on the download link, there is no recognition of a download happening and when I check my files later I have an "internet" file showing with a title but without a video file extension and nothing will open. The file extension is ".html". I am following the step by step instructions from the site involved. Other sites videos are downloading as expected.

Does firefox need to be my default browser? Any suggestions how to remedy this without losing what is working? Are there plug-ins that can address this issue?

Thanks.