run this in your browser's console to display all font-family properties used on the site styled in that font-family

font-demo.js

{
  const fonts = new Set()

  document.querySelectorAll('*').forEach(tag => fonts.add(getComputedStyle(tag).fontFamily))

  console.log(fonts)

  document.body.insertAdjacentHTML('beforeEnd', `
    <font-demo>
      <style>
        font-demo {
          display: block;
          font-size: 10pt;
          padding: 4em;
          background: white;
        }
        font-demo h1 {
          display: block;
          font-size: 24pt;
          margin: 1em auto;
          line-height: 1.2;
          color: black;
        }
        ${
          Array.from(fonts).map((font, index) => `
            font-demo h1:nth-of-type(${index + 1}) {
              font-family: ${font} !important;
              font-weight: bolder;
            }
          `).join('\n')
        }
      </style>
      ${Array.from(fonts).map(font =>
        `<h1>${font}</h1>`
      ).join('\n')}
    </font-demo>
  `)
}