If you still wish to attempt an installation for archival or collection purposes, these are the methods historically used by the Legacy Jailbreak community:
The mobile site uses standard web protocols that are more likely to be compatible with older browsers than the proprietary API calls used by the 2011-era app. facebook messenger ipa for ios 4.2.1 download
You can still send and receive basic text messages via the mobile web interface without needing a separate Messenger app. Troubleshooting Potential Issues Operating systems that support the Messenger app - Facebook If you still wish to attempt an installation
Use a tool like iFunBox on a PC to drag and drop the .ipa file into the "User Applications" directory of your device. facebook messenger ipa for ios 4.2.1 download
Install from a repository such as cydia.akemi.ai .