test-tampermonkey.js

run = 0;

actionFunction = function() {
    if (run === 0) {
        $('.comment_input_wrapper .body .options').after($('<button id="unsubscribe" class="origin btn">Unsubscribe</button>'));

        $('#unsubscribe').click(function(){
            alert($('.sender').find('a').html());
        });
        
        run = 1;
    }
};

waitForKeyElements(".comment_input_wrapper", actionFunction);