This plugin has not been updated by its developer since a long time ago.
It could imply partial or total lack of compatibility with the latest versions of b2evolution.
Footnotes is a footnote plugin for b2evolution. It lets you add unobtrusive side/snide/additional/informative remarks without getting in the way of the main text. So far, it supports two ways of rendering those footnotes: via tooltips using MooTool's Tips library or via plain anchor jumps using <a href> and <a name>.