Search engines often can't index content that relies on browser plugins, such as Java or Flash. That means plugin-based content doesn't show up in search results.
Also, most mobile devices don't support plugins, which creates frustrating experiences for mobile users.
How the Lighthouse plugins audit fails #
Lighthouse flags pages that use plugins:
Lighthouse checks the page for elements that commonly represent plugins:
Lighthouse then flags an element as a plugin if its MIME type matches any of the following:
Lighthouse also flags elements that point to a URL with a file format that is known to represent plugin content:
Don't use plugins to display your content #
To convert plugin-based content to HTML, refer to guidance for that plugin. For example, MDN explains how to convert Flash video to HTML5 video.