Praise be to Allah, the Lord of the worlds.
It is desirable (Mustahab) for a Muslim to offer two Rakahs before the first Athan of Jumu`a (Friday) prayer since the Messenger of Allah said: "There is a Salat (prayer) between every Adhan and Iqamah; there is a Salat between every Adhan and Iqamah." While saying the same for the third time, he added: "It is for him who desires to perform it" {Al-Bukhari & Muslim}.
The Imams of the four legal schools agreed that it is desirable, but some disagreed about the specific number of Rakahs and about considering it from Al-Sunan al-Rawatib (Sunnah Mu'akkadah). Actually, this disagreement is insignificant since there is consensus that it is desirable.
Ibn Rajab {May Allah have mercy on him} said: "At the time of Zawal on Friday, before the Imam climbs the Minbar (pulpit), it is desirable to offer the Sunnah prayer, and this is agreed on by all scholars. In fact, none of them has ever said that it is disliked (Makrooh), because saying so violates their consensus. In addition, he (Ibn Rajab) mentioned many narrations in favor of this position. Then, he said: scholars disagreed about whether it is from Al-Sunnan Al-Rawatib, such as the two Rakahs before Duhr prayer, or desirable, such as the Sunnah prayer offered before Asr? Most of the scholars, such as Al-Awzai`, Al-Thawri, Abu Hanifa and his fellow scholars, are of the view that it is from Al-Sunnan Al-Rawatib,….However, many late Hanbali scholars said that it isn`t. Rather it is desirable." {Fateh Al-Bari, vol.5/pp.541}. And Allah Knows Best.