In order to compress and decompress video streams, browsers need to handle various codecs. For patent reasons, Firefox couldn't encode/decode H.264 without external (separate) help, and this was a problem because H.264, used in MP4 video, is very popular. Cisco released an open source (patent-free) decoder that is now distributed with Firefox.

By itself, the Cisco plugin doesn't do anything, but it can be used for browser-to-browser communications (WebRTC), and in the future perhaps for website videos.

If you prefer that the plugin be disabled until its usefulness is clearer, you can set it to "Never Activate" on the Add-ons page.

See also:

• http://andreasgal.com/2014/10/14/openh264-now-in-firefox/

Thank you both! I wasn't sure what all it did.