Allowed domains (like Twitter) on my Content Filtering policies are not working

Websites that I configured in allowed domains (like Twitter) on my Content Filtering policies are not correctly displayed

 

For this scenario we will see a CFS policy which denies social networking but allows twitter.com

Now this normally should be everything that you need to do to have this working, but if you try to go to twitter.com you will see that the website is not correctly displayed.
If we analyze the source code of that website, we see that it uses resources from another domain (abs.twimg.com)  We need to add that domain to the allowed domains and now twitter will be correctly displayed.

Since every website have their own source code, sometimes it will be needed to do this troubleshooting (to see the source code and look for other domains) to solve similar issues.