For reference for anyone tuning in, in order to get the full quality image from an Instagram page, you have to (in a Firefox-based browser):
bring up the menu box on the webpage of the image that has been focused (because you cannot click on the image directly and do "Save Image"), and activate "View Page Info".
Then, you have to navigate to the "Media" tab in the following window that will open.
Once that's done, you will be able to scroll for the full size image amongst the many that will pop up. What you're looking for is usually near the bottom of the list. When you find it, you'll see information that shows what the resize you're looking at is, and the dimensions of the original image alongside that. Save that image and you have the full quality.