Here is the latest article on facebook where you later can zoom your photos on facebook. His name is PhotoZoom and specifically for users of Mozilla because this is the add-ons.

Like what up PhotoZoom this?, later you can see the preview, but that certainly is a special add-ons for Facebook which is able to zoom to your friend's profile photo or a photo you just added by your friends.

The bottom line up PhotoZoom will enlarge each photo that is on up the same as the original size, if we point the mouse to one of the photos on Facebook for example like this.
If you are interested to use it, Please Direct Download via its source here, When you're done be sure to restart your browser and then open your facebook profile to make sure the Add-Ons up PhotoZoom already functioning.