Enable PDF.js
Supported on: Firefox 77 or later
Registry
HKLM
Software\Policies\Mozilla\Firefox\PDFjs HKCU
Software\Policies\Mozilla\Firefox\PDFjs Value name: Enabled
Enabled: Enabled = 1
Disabled: Enabled = 0
Description
If this policy is disabled, the built-in PDF viewer is not used. If this policy is enabled or not configured, the built-in PDF viewer is used.