Bigfoot is a nice jquery plugin to display footnotes inspired by Inspired by Instapaper.. It will display a dots symbol on footnote position and display footnotes on small popup. The script and default styles are built to work great on any size viewport; the popover will be positioned on the top/ bottom automatically (based on the relative amount of space), will update its location as the viewport changes size, and will ensure that the popover never scrolls offscreen. All of that adds up to a much-improved user experience.
It auto-detects the footnote link + content, converts the link into a button and displays the footnote content inside a popover when clicked.
This script is provided under the MIT License.