Specifically, instead of directly providing numbers in html,
they do this <span class="wgb_arv">У</span><span class="wgb_arv">Ф</span><span class="wgb_arv">Р</span></b>
<br>ж</td> which supposed to be an integer number. Apparently they have more than one way of doing that.
To counter adblockers Facebook puts the text "Sponsored Ad" in multiple span, like each letter in a different one, so it's harder to blocks those posts on the timeline.