The E90 has limited RAM (128 MB). To avoid crashes while browsing Facebook, close all background apps and use the internal widescreen for a better "desktop-like" experience.
To get Facebook running on your E90 today, you must use specialized browsers or third-party Java-based clients that handle modern encryption. facebook app for nokia e90
Ensure your phone's date and time are accurate. If they are off, security certificates will fail, and no app will connect to the internet. The E90 has limited RAM (128 MB)