jsonObject

String or Array or Object. The object to display. If this is an object it is JSON-serialized, so properties like functions will be omitted.

rootTitle Optional

String. The title of the root of the tree in which the object is displayed.

A Promise that will be fulfilled with no arguments, once the object has been set.

Create a new pane, and populate it with a JSON object. You could run this code in a script loaded by your extension's devtools page.

function onCreated(sidebarPane) {
  sidebarPane.setObject({
    someBool: true,
    someString: "hello there",
    someObject: {
      someNumber: 42,
      someOtherString: "this is my pane's content"
    }
  });
}

browser.devtools.panels.elements.createSidebarPane("My pane").then(onCreated);