This is an already implemented feature on Edge, Chrome, Safari and even Opera. When you drag drop images from WEB pages to folder or apps, Firefox keeps pasting URLs instead of images real files. Please add this feature as it's super useful.
This should have hundreds of up-votes. The current behavior of saving as a URL causes grief for unsuspecting users. They expect to get a file when dragging to a folder.
What you get when dragging with Firefox depends on the content. Sometimes you'll get a URL (with a long name that is difficult to delete) and sometimes you'll get a file. I can recreate the URL issue if the web item is a base64 encoded image. Chrome based browsers always yield a file for base64 links.