JS embedding isn't unique to Firefox. This is Firefox catching up with an old feature from Adobe Acrobat. PDFs with embedded JS have been Turing complete for ye

JS embedding isn't unique to Firefox. This is Firefox catching up with an old feature from Adobe Acrobat. PDFs with embedded JS have been Turing complete for years, in readers that run the JS. Just like PDFs with embedded Flash content. The PDF layout language isn't Turing complete on its own.