removeSponsoredPostsInFacebook.js

function realText(elem) {
	if (elem instanceof Text) {
		return elem.textContent;
	}
	const visibleText = [...elem.childNodes]
		.filter(elem => elem instanceof Text || window.getComputedStyle(elem, "").display !== 'none')
		.flatMap(elem => realText(elem))
		.join('')
	return visibleText
}
function isSponsored(elem) {
	return elem && realText(elem).toLowerCase().startsWith('sponsored')
}
function isArticleSponsored(elem) {
	return isSponsored(elem.querySelector('div[id^=feed_subtitle]'))
}
const domInsertionObserver = new MutationObserver(function(mutationsList){
  [...mutationsList]
    .filter(mutation => mutation.type === 'childList' && mutation.addedNodes.length)
    .flatMap(mutation => [...mutation.addedNodes])
    .filter(addedNode => typeof addedNode.id === 'string' && addedNode.id.startsWith('u_fetchstream'))
    .filter(isArticleSponsored)
    .forEach(post => post.parentElement.removeChild(post))
});
domInsertionObserver.observe(document.querySelector('div[id^=feed_stream]'), { childList: true, subtree: true });