So where did you download sliverlight from? And did you remove the pluginreg file before just deleting it instead? Messing with Registry file is something you have to be very careful it's not something you mess with until last resort. Does it tell what components it needs? If you need silverlight here is the last latest version. Download it and install it-if need be.

https://www.microsoft.com/silverlight/

<strike>https://www.softexia.com/web-apps/silverlight</strike>

edit: added official source url.

You can no longer use the Silverlight plugin in current Firefox releases, but Netflix should use the HTML5 media player in Firefox.

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

• Options/Preferences -> General: Play DRM
• https://support.mozilla.org/en-US/kb/enable-drm
• https://www.ghacks.net/2016/04/11/firefox-drm-and-the-end-of-npapi/

Firefox 52 and later releases only support the Shockwave Flash plugin and disable all other plugins.

Why-do-Java-Silverlight-Adobe-Acrobat-and-other-plugins-no longer work.

• https://support.mozilla.org/en-US/kb/npapi-plugins

Cheers, toggling the DRM worked. I've spent so long googling trying to find a fix and it was so simple.