Many websites use several domains and/or hostnames (subsites) to improve the speed of loading. You should consider it when you're adding some websites to blacklist or whitelist.
Therefore, if you have blocked the category, but want to have access to some website from the blocked category, you should include all subsites of this website on the whitelist.
To find the list of subsites of a website you can use a development console in your web browser.
Here are the examples of subsites for some popular websites that you should add to the whitelist while the main category for these sites or services is blocked. Please note, that sites' owners can change these addresses from time to time.
- youtube.com (without www)
- facebook.com (without www)
- skype.com (without www)
- twitter.com (without www)