“License request failed” with any site that uses DRM

DRM in Firefox is delivered through a plugin by Google's Widevine Platform. You can find it in about:addons, looking for the "Widevine Content Decryption Module provided by Google Inc.".

There's a bug in Firefox which has peen patched only from V. 88 forwards. It causes Widevine to break on versions below that since the moment Widevine has retired older versions of its Content Decryption Module: see this thread. However there seems to be (or at least was) a workaround which I've found in this thread, and which might still work:

• in your profile folder, locate \gmp-widevinecdm\4.10.2391.0\manifest.json (the version of your widevine install might differ)

• edit the manifest.json, and at "x-cdm-codecs" substitute "vp09" with "vp9.0" (which is the old flag from earlier Widevine versions).

I'm not able to test the workaround right now, but it should be easy to do on your install. If this doesn't work, there are good chances that you won't be able to get DRM Content working in FF 86.

Please understand that DRM is officially supported only in the latest 3 versions of Firefox. For Chrome, Google seems to have been pushing this practice for some time now, and they will continue to retire older versions of Widevine, as they don't seem to have any interest in supporting older platforms.