mouseover-zoom for rich footnote images
When an image is attached to a rich footnote it is possible to left-click once to open a "big thumbnail" as a kind of small overview which is fine. Many times one would need a detailed zoomed view. This should be possible left-clicking again into the "big thumbnail" and then dragging the mouse pointer around on the "big thumbnail area" keeping the mouse button pressed. "Directory Opus 12" filemanager has this implementation and it is very useful. Instantly available when needed, never in the way. The full screen size is used for magnification without any frame around. As soon as the mouse button is released the zoom window disappears.
As another mechanism when the mouse pointer hovers over the link for n milliseconds (please allow user to customize this value) a zoomed view would open in a popup window and dragging around the mouse would again change the magnification area.