Change Layout of default JSON viewer through Add-On?

Hello community,

I’d like to change the layout of the default JSON viewer in Firefox (about:config --> devtools.jsonview.enabled --> true).

I know it’s possible via:

  • Create a userContent.css file (within chrome folder in the profile)
  • Set toolkit.legacyUserProfileCustomizations.stylesheets to true in about:config
  • Restart Firefox

But I’d like to apply CSS changes via an Add-On and to me it looks like that neither content scripts nor user scripts are working when the default JSON viewer is loaded.

Do you have any further information?

Best regards


I think the JSON viewer is devtools code, and as such privileged. It being privileged means that you can’t directly interact with it as webextension.

Thanks. That’s not want I want to read but it sounds comprehensible :wink:

Extensions can intercept certain files as they come in, and show them in their own extension pages. It’s been a while since I’ve used it, but I know of at least one RSS reader extension that does that: