The actions need to be actual names not numbers.

Have you taken a look at Handlers here?

https://mozilla.github.io/policy-templates/#handlers

Also, JNLP only works on the ESR (long story)

Thank you for that information! So the handler action can be a number in the local Handlers.json in the local profile, but not in the GPO, got it. I guess there is simply not an action for "open in browser" or "handle internally"..?

> I guess there is simply not an action for "open in browser" or "handle internally"..?

Yeah, I figured most of those would just happen by default. Have you found a case where I need to add it?

I'm guessing webp, avif, and PDF are, by default, set to open in browser and my broken policies are changing them to save to file? So I just need to set a GPO handler for JNLP only, I think (I am on ESR102.7) This should work for the JNLP handler GPO, right? Thanks again for your time and support!!!

{

 "mimeTypes": {
   "application/x-java-jnlp-file": {
     "action": "useHelperApp",
     "ask": false,
     "handlers": [{
       "name": "Java(TM) Web Start",
       "path": "C:\\Program Files (x86)\\Java\\jre-1.8\\bin\\javaws.exe"
     }]
   }
 },
 "extensions": {
   "jnlp": {
     "action": "useHelperApp",
     "ask": false,
     "handlers": [{
       "name": "Java(TM) Web Start",
       "path": "C:\\Program Files (x86)\\Java\\jre-1.8\\bin\\javaws.exe"
     }]
   }
 }

}

Yeah, you shouldn't need to modify anything for the other stuff.

And yeah, those should definitely work for jnlp.,

Thank you so much, Mike!