If your Facebook videos are taking too much time to buffer or your streaming quality is poor, this may be due to a slow internet connection. If so, you can boost your computer's performance by refreshing your page, closing other tabs, or stopping background downloads. Alternatively, you can also configure Facebook to stream videos in SD only (Standard Definition) format.
Connect to your Facebook account and click on Settings:
Go to the Videos section:
Next to Video Default Quality, select SD Only: