webextensions-examples/permissions/page.js

function updatePermissions() {
  browser.permissions.getAll()
  .then((permissions) => {
    document.getElementById('permissions').innerText = permissions.permissions.join(', ');
  });
}

async function processChange(event) {
  let permission = event.target.dataset.permission;
  let result = document.getElementById('result');

  try {
    if (event.target.dataset.action === 'grant') {
      browser.permissions.request({permissions: [permission]})
      .then((response) => {
        result.className = 'bg-success';
        result.textContent = 'Call successful.';
      })
      .catch((err) => {
        // Catch the case where the permission cannot be granted.
        result.className = 'bg-warning';
        result.textContent = err.message;
      });
    }
    else {
      browser.permissions.remove({permissions: [permission]})
      .then((response) => {
        result.className = 'bg-success';
        result.textContent = 'Call successful.';
      });
    }
  } catch(err) {
    // Catch the case where the permission is completely wrong.
    result.className = 'bg-danger';
    result.textContent = err.message;
  }
  result.style.display = 'block';
  updatePermissions();
  event.preventDefault();
}

for (let element of document.getElementsByClassName('permission')) {
  element.addEventListener('click', processChange);
}

updatePermissions();