Run this while viewing someone's Twitter /following list to get the handles of everyone they follow

followers.js

let $follows = document.querySelector('div[data-testid="primaryColumn"] section > h1 + div[aria-label] > div')
let handles = new Set()
let finishTimeout
let observer

function finish() {
  if (finishTimeout) {
    clearTimeout(finishTimeout)
  }
  finishTimeout = setTimeout(() => {
    console.log(Array.from(handles).join(', '))
    observer.disconnect()
  }, 10000)
}

function processFollows() {
  for (let $follow of $follows.children) {
    if ($follow.firstElementChild.style.display === 'none') {
      continue
    }

    let $handle = $follow.querySelector('a:not([aria-hidden])[tabindex]')
    if ($handle) {
      handles.add($handle.innerText)
      $follow.firstElementChild.style.display = 'none'
    }
  }

  console.log(handles.size)
  finish()
}

observer = new MutationObserver(processFollows)
observer.observe($follows, {childList: true})
processFollows()