I think I finally got Firefox figured out. Here's what I did to save a picture off eBay:
1: Enlarge the picture on eBay
2. Right-click the picture to get the pop-up menu, then left-click on "View Page Info"
3. Left-click on the "Media" icon at the top of the "Page Info" pop-up page
4. Left-click on the "Save As" button towards the bottom of the page, on the right side
5. Browse to the folder of your choice, name the file, and save it