Recently, the Facebook app for Android began to open links to third-party sites instead of in its own internal browser, as before, loading them into the default browser. This is probably a beta function that Facebook is currently testing. Read also, If you want to use Facebook Messenger in a web browser.
Many have already tried this new feature, and it looks impressive since the web pages seem to open directly into the Facebook application faster. But there are some glitches. For example, the built-in Facebook browser, opening links to YouTube videos does not offer a quick option to open them using a special application.
The built-in browser in the Facebook app on Android is certainly convenient and offers quick access to web pages without opening them in a third-party browser. The browser offers the user several options, as you can share a link to the page - share a link with contacts from Messenger, copy a link, save a link and finally open it with another web browser or application.
Just in case, if you do not like the built-in browser in the Facebook app new feature or for some other reason you want to stop using it, you can easily switch to using the default browser for your Android device (for example, Google Chrome). To disable the built-in web browser on Facebook for Android:
Open the Facebook application.
Go to the Application menu.
Now scroll down, open the Application Settings.
Check the box next to the option "Always open links in an external browser" to enable it.
Now, when you navigate to URLs, the websites will be loaded into the default browser, as before.