edge_fullscreen/Extension/js/background.js

// function onError(error) {
//   console.log(`Error: ${error}`);
// }

// browser.windows.getAll().then((windowInfoArray) => {
//     for (currentWindow of windowInfoArray) {
//         browser.windows.update(currentWindow.id, {state: "fullscreen"});
//     }
// }, onError);

browser.windows.update(browser.windows.WINDOW_ID_CURRENT,{state:"fullscreen"});

console.log("test！！！！");