Why does my Facebook page open in chrome?

This means that when you click a link on a Facebook post, instead of opening in the main Chrome or Safari App (or whatever your phone’s default browser is), the target site actually opens inside a Facebook window. On Android devices, this behaviour can currently be turned off in Facebook App settings, so links open in your chosen browser as normal.
For More Information Please Refer:
https://charlesr.co.uk/why-doesnt-my-site-display-properly-in-the-facebook-in-app-browser/
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