A full browser screenshot is always more helpful. It would allow us to see your add-ons. see screenshot Did you try with Firefox in Safe Mode? https://support.mozilla.org/en-US/kb/diagnose-firefox-issues-using-troubleshoot-mode

What security software are you running?

Make sure you have updated the Widevine plugin to the latest version (4.10.2557.0).

• Tools -> Add-ons -> Plugins

You can toggle DRM off/on to see if that makes Firefox (re)load DRM components.

• Settings -> General: Play DRM
• https://support.mozilla.org/en-US/kb/enable-drm

You can possibly check the XHR requests in the Browser Console if this doesn't work.

• https://developer.mozilla.org/en-US/docs/Tools/Browser_Console