Chrome bundles the Flash Pepper plugin, but Adobe's Flash NPAPI plugin installer also bundled Chrome as an opt-out "make Chrome my default browser" setting. So

Chrome bundles the Flash Pepper plugin, but Adobe's Flash NPAPI plugin installer also bundled Chrome as an opt-out "make Chrome my default browser" setting. So a Firefox user downloading the Flash NPAPI plugin (for their Firefox) would, by default, end up downloading the Flash NPAPI plugin, Chrome, and Chrome's Flash Pepper plugin. If the user really wanted Chrome, they would have downloaded it instead of downloading Flash NPAPI plugin that works in Firefox and not in Chrome.