Is it permissible to combine the Friday prayer with the Asr prayer, and why during Qunut behind the imam do worshippers say Amin to some parts but recite other parts themselves?

Summary

Scholars differ on combining Friday prayer with Asr. The first view permits it by analogy of Friday prayer with Zuhr; it is the Shafii position endorsed by al-Suyuti and relied upon by al-Zarkasyi, and it is the view favoured in this answer because its argument is strong and there is public benefit. The second view forbids it, since acts of worship are based on textual fixity and cannot be extended by analogy; it is the well-known Hanbali view and also one opinion within the Shafii school. In Qunut, followers say Amin to the imam's supplication, but some phrases are praise of God's power rather than a request, so followers recite them as well.

Written in our own words from the original fatwa — check the source before acting on it.