Manually Install OpenH264 codec for Firefox

This post shows how to install the OpenH264 Video Codec in Firefox. It’s useful when Firefox fails to install it automatically, or for fine-tuning the version you want.

The solution below, found by referencing a previous profile, is as follows:

Download a relevant release from Cisco’s openh264 RELEASES page.
Open with an archiver and extract the .dll to %appdata%/mozilla/firefox/profiles/xxxxx.default/gmp-gmpopenh264/1.2 (change 1.2 to your desired version).
Rename the extracted file to gmpopenh264.dll.
Create a new file in that directory called gmpopenh264.info. Edit it and add:

Name: gmpopenh264
Description: GMP Plugin for OpenH264.
Version: 1.2
APIs: encode-video[h264], decode-video[h264]

Open prefs.js in the Firefox user folder and add:

user_pref("media.gmp-gmpopenh264.version", "1.2");

After following these steps you will have the OpenH264 codec enabled.