https://addons.mozilla.org/en-US/firefox/addon/devtools-media-panel/
This a web extension adaption of the aboutmedia addon https://github.com/jyavenard/aboutmedia
It creates a new 'Media' tab in the Firefox developer tools panel - currently supported in Firefox 54+
Instructions for installing manually:
- Clone/download repo
- Open Firefox
- Go to 'about:debugging'
- Click 'Load Temporary Add-on' button
- Navigate to 'extension' subdirectory in repo
- Open any file in this directory
- There should be a new 'Media Panel' addon listed under 'Extensions'
- Navigate to page with video element and open developer tools (F12)
- There should be a new 'Media' tab