DLL for Firefox 52.9.0 ESR in 32-bit Windows XP?

[Newbie]

I have an old Dell PC that I am adapting for home theater, but cannot stream video from Kanopy.com due to a DRM issue. Although that site says Firefox v.47+ is required, apparently v.52 ESR won't work, and there is no menu to follow their instructions, "In Firefox, go to about:preferences and ensure "Play DRM-controlled content" is enabled, and that about:addons (in the plugins tab) Widevine is enabled."

From another forum, I tried updating Firefox config with 32-bit widevine v. 1.4.9.1088, but apparently that is too advanced, and didn't do anything. My questions are:
1. Which version of widevinecdm should I use, and can someone link me to it?
2. Is there anything (e.g. in regedit) I should do to replace the bad version, or will revising the entry in Firefox config update automatically?
Thank you.