Thanks to Tushar Shahi for helping me...

async function cookieTest() {
    const getTab = new Promise((resolve, reject) => {
        function logTabs(tabs) {
            resolve(tabs[0].url);
        }
        
        function onError(error) {
            reject(error);
        }
        
        browser.tabs
            .query({ currentWindow: true, active: true })
            .then(logTabs, onError);
    });

    getTab.then(res => {
        console.log(res);
        setCookie(res);
    }).catch(err => {
        console.log(err);
    });
}

async function setCookie(currentUrl) {
    console.log(currentUrl);
    const storeCookie = new Promise((resolve, reject) => {
        function cookieSet() {
            resolve("cookie set");
        }
        
        function onError(error) {
            reject(error);
        }
        
        browser.cookies
            .set({
                url: currentUrl,
                name: "SID",
                value: "1234",
            })
            .then(cookieSet, onError);
    });
    
    storeCookie.then(res => {
        console.log(res);
        function logCookie(cookie) {
            if (cookie) {
                console.log(cookie.value);
            }
        }
        let getting = browser.cookies.get({
            url: currentUrl,
            name: "SID",
        });
        getting.then(logCookie);
    }).catch(err => {
        console.log(err);
    });
}