Rated 4 out of 5 stars
For many years Image Zoom was one of my favorite addons. Even if it worked only partially, recently. As the last entry on the project homepage dates from 2013, there is no hope for an upgrade to WebExtensions & FF 57 Quantum. So it seems to be the time to say goodbye - sadly!
UPDATE: I have found a nice addon to replace "Image Zoom": it is called "Zoom Image".