It wasn’t all perfect. The app famously broke every time Facebook updated its API. You’d open the app to see: "Network Error: Connection timed out."
Facebook actually ran a mobile site ( m.facebook.com ) that offered an app download link. If you visited that page on the E71’s WebKit browser, it would detect your Symbian OS and serve you a .sis or .sisx file.
A: No. The standalone Messenger app never released for Symbian v3. The integrated chat within the main Facebook app died in 2015. Use mbasic.facebook.com in Opera Mini for basic messaging.