I used the code generated on this page:
https://developers.facebook.com/docs/reference/plugins/comments/
However, since my pages are dynamic I replaced this part:
<div class="fb-comments" data-href="http://example.com" data-width="470" data-num-posts="10"></div>
with...
<div class="fb-comments" data-href="http://www.mywebsite.com/index.php?a=[some dynamic name]" data-width="470" data-num-posts="10"></div>
When I try to post, the comment would show up but when I refresh the page, it would disappear. Am I doing something wrong?