Use mouse wheel to zoom in on images "inline" - that is - without a popup.
Hover on some image / video, press shift and use mouse wheel to zoom in and out.
Once you zoom in/out on an element, this element becomes draggable, useful in case the element is partially hidden (doesn't fit in its container).
The extension is listed on AMO - https://addons.mozilla.org/firefox/addon/in-zoom/
The extension is listed on Chrome Web Store - https://chrome.google.com/webstore/detail/in-zoom/oppcghdbglmbhhobfoodedhokbadlenh