After several attempts and some searching, I figured out what the configuration to run a script in fiddle is.

Ensure you have the following options set.

1. For the HTML section.
   • Select the HTML 4.01 Strict option.

      2. For the JavaScript section

• Select No wrap -body

I did this in Firefox Quantum 59.0.1 (64-bit) for Linux , but it should work on a different OS.

Thanks!