When you download files in your web browser, is it hard to find where they ended up on your computer?
If so, you can tell Firefox where you want all your downloads to be stored. In many cases, it might be easiest to have them downloaded to your computer's Desktop so they're easy to find.
If you need to track down previous downloaded files, go to Tools > Downloads and use the search box to find your file. Once you’ve found it, double-click on the file to open it, or right-click and choose "Copy Download Link".