details

object. An object optionally containing the windowId to check.

windowId Optional

integer. ID of a browser window to check. If omitted defaults to windows.WINDOW_ID_CURRENT, which refers to the topmost browser window.

A Promise that will be fulfilled with true if the extension's sidebar is open in the given window, or false otherwise.

Check the topmost window:

browser.sidebarAction.isOpen({}).then((result) => {
  console.log(result);
});

Check all open windows:

async function checkWindow(windowId) {
  const result = await browser.sidebarAction.isOpen({ windowId });
  console.log(`window: ${windowId} status: ${result}`);
}

browser.windows.getAll().then((all) => {
  for (const { id } of all) {
    checkWindow(id);
  }
});