sidebarAction.open()

You can only call this function from inside the handler for a user action.

This is an asynchronous function that returns a Promise.

None.

A Promise that is resolved with no arguments.

Open the sidebar when the user selects a context menu item:

browser.menus.create({
  id: "open-sidebar",
  title: "open sidebar",
  contexts: ["all"]
});

browser.menus.onClicked.addListener(() => {
  browser.sidebarAction.open();
});