var instance = document.getElementById('instance')

instance.addEventListener('onchange',function (event){
    browser.storage.sync.set({'value':event.target.value});
});
document.getElementById('save').addEventListener('click',function(event){
    browser.storage.sync.set({'value':instance.value});
});

document.addEventListener('DOMContentLoaded',function(){
    browser.storage.sync.get('value').then(
    result => instance.value = result.value,
    err => instance.value="Error.")
});