Try changing DNS over HTTPS (DoH) to "Off" or "Max Protection" and in Connection Settings change "Use system proxy settings" to "No proxy".

Also try disabling any third-party antivirus or security software.

Ah, nope, sadly it did not work. It's driving my mother insane :D

There's no third party antivirus or adblocks enabled. Which is sketchy at best but the woman is elderly and just wants to watch murder mysteries. :D

Philo sends out this error:

Source: ERROR_SOURCE_SHAKA_PLAYER

UserAgent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:122.0) Gecko/20100101 Firefox/122.0

Session Details:

{

 "assetType": "recording",
 "assetId": "UmVjb3JkaW5nOjYwODU0ODg5OTg5NjUyMDE1NA",
 "playbackSessionId": "web-4aa8aa90-bd38-11ee-bc09-e7a35687a6f3",
 "sharedPlaybackSessionId": "U2hhcmVkUGxheWJhY2tTZXNzaW9uOjAtd2ViLTgyZWM1YzY5LTFkNzktNGY2Yy1hZjYwLTk2OTFhZTZiNDQ1Mg",
 "manifest": "https://www.philo.com/manifestv2/dvr/608548899896520154/manifest.json?content_host=prod.cdn-fsty.philo.com&dspid=web-4aa8aa90-bd38-11ee-bc09-e7a35687a6f3&sdpid=0-web-82ec5c69-1d79-4f6c-af60-9691ae6b4452&sdsn=1"

}

Error Details:

{

 "severity": 2,
 "category": 6,
 "code": 6007,
 "data": [
   {
     "severity": 2,
     "category": 1,
     "code": 1001,
     "data": [
       "https://lic.drmtoday.com/license-proxy-widevine/cenc/",
       406,
       "<title>HTTP Status 406 – Not Acceptable</title><style type='\"text/css\"'>body {font-family:Tahoma,Arial,sans-serif;} h1, h2, h3, b {color:white;background-color:#525D76;} h1 {font-size:22px;} h2 {font-size:16px;} h3 {font-size:14px;} p {font-size:12px;} a {color:black;} .line {height:1px;background-color:#525D76;border:none;}</style>
HTTP Status 406 – Not Acceptable
",
       {
         "content-language": "en",
         "content-length": "441",
         "content-type": "text/html;charset=utf-8",
         "x-dt-client-info": "eyJtYW51ZmFjdHVyZXIiOiJHb29nbGUiLCJtb2RlbCI6IkNocm9tZUNETS1XaW4teDY0LTEwIiwiZHJtVmVyc2lvbiI6IjQuMTAuMjU1Ny4wIiwic2VjTGV2ZWwiOjMsImhkY3BTdXBwb3J0IjoiSERDUF9WMSIsInZyQ29uc3RyYWludFN1cHBvcnQiOnRydWV9",
         "x-dt-li": "eyJ0aSI6IjlkNzIyNzMxZmRiZmExYWMxM2Q3ZTk5MmRjYmEzOWY1In0=",
         "x-dt-resp-code": "40001"
       },
       2
     ],
     "handled": false
   }
 ],
 "handled": false

}

Make sure you the latest Widevine version (4.10.2710.0).

• Tools -> Add-ons -> Plugins

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

• Settings -> General: Digital Rights Management (DRM) Content
• https://support.mozilla.org/en-US/kb/enable-drm

Make sure you the latest Widevine version (4.10.2710.0).

• Tools -> Add-ons -> Plugins

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

• Settings -> General: Digital Rights Management (DRM) Content
• https://support.mozilla.org/en-US/kb/enable-drm

This fixed it! Thank you so much! My mom is extremely happy.