You can create a Policy File on Linux named "/etc/firefox/policies/policies.json" to disable pdf through out the system, here is a snippet for just pdf:

{ "policies": { "PDFjs": { "Enabled": false }, "DisableBuiltinPDFViewer": true } }

See:

https://support.mozilla.org/en-US/kb/managing-policies-linux...

I see pdfjs.enableScripting in about:config options. Have to check whether that option disables this scripting after I get the new version.