How do you make a picture already uploaded onto FB a profile picture?

[star R]

The photo usually has to be your own for it to be available as your profile picture, depending on security and privacy settings. If you do not see the option to "Make this photo my profile picture" then you will need to download the photo and re-upload it as your own photo.

Right-click on the image and save it to your computer. Then upload and make your profile picture as usual.

NOTE: You cannot right-click and save images in the new FB image pop-up feature. To get around this, when the photo pops up, look in the browser bar and delete the "&type=1&theater" from the end of the address. This will bring the image up in a regular FB browser page, where you can right-click and save the photo.