By default, the Facebook app uses an in-app browser to open links in their web view. If you would prefer to open links in their full view, here's a quick tutorial on how to turn off Facebook's in-app web browser.
How To Disable Facebook's In-App Browser
Tap on a link to open it in web view. Then tap on the More button (represented by 3 vertical dots) > Open in Browser:
Make Facebook Open Links in Browser
You can also configure the Facebook app to automatically open links with your smartphone's default web browser.
Open the Facebook app, and tap on the Menu button.
Click on the Help and Settings section, and tap on App Settings:
Go to General Settings and enable the Links open externally option: