It sounds like you're looking for information on a very specific, older piece of software: the (which used .sis or .sisx files).

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A: Facebook removed it from their servers in 2015. It is abandonware now, meaning it is legal to download for archival purposes, but Facebook offers no support.

No known functional Facebook SIS file works in 2025. Facebook now requires HTTPS + TLS 1.2+ and modern OAuth, which Symbian lacks.