Preferences Saving for Thunderbird

I would to save preferences for a WebExtension addon for Thunderbird.
I tried to use‘preference1’); but I get error “ is undefined”. I added the permission “storage” in manifest.json.
How can I store users preferences for my WebExention addon ?

Finally I made it work, the correct syntax is
function failureCallback(error) {
console.error("Error " + error);
function success(itemValue) {
var value = itemValue.preference1;
let promiseValue =[‘preference1’]);
promiseValue.then(success, failureCallback);