JavaScript snippet to unlike all your liked activity on FaceBook

unlike.js

function startIt()
{
    document.querySelectorAll(".mrs._2fmu.img.sp_XaQA31b2wGR_2x.sx_06c0ed")[0].click();
    setTimeout(function()
    {
        [].slice.call(document.querySelectorAll("a[rel='async-post'][role='menuitem']")).pop().click();
        
        setTimeout(startIt, 2000);
    }, 1000);
}

startIt();

// works best if you go to your FB pages activity page and then filter on "Likes"
// and then scroll all the way down until it loads everything and then run the above

// sometimes it gets stuck so you might have to reload the page and start over