Usernames CAN contain periods, but they're currently not supported. There's also no need for a trailing slash.
Example: https://www.facebook.com/RaiPlay.it/videos/
1059491774481091
</provider>
<provider name="facebook-video">
<title>Facebook Video</title>
- <regex><![CDATA[(?<HREF>https?://(www\.)?facebook\.com/watch/\?v=(?<ID>[0-9]+))
-(?<HREF>https?://(www\.)?facebook\.com/[a-zA-Z0-9_-]+/videos/(?<ID>[0-9]+)/)
+ <regex><![CDATA[(?<HREF>https?://(www\.)?facebook\.com/watch/?\?v=(?<ID>[0-9]+))
+(?<HREF>https?://(www\.)?facebook\.com/[a-zA-Z0-9_\.-]+/videos/(?<ID>[0-9]+))
(?<HREF>https?://fb\.watch/(?<ID>[a-zA-Z0-9_-]+)/)]]></regex>
<html><![CDATA[<div class="fb-video" data-href="{$HREF}" data-allowfullscreen="true">{$HREF}</div>
<script>require(['WoltLabSuite/Core/Wrapper/FacebookSdk'],function(FB){FB.XFBML.parse()})</script>]]></html>