Start a game as Egypt. Build 2 workers then Stonehenge. Build a barracks and lots of warriors. Improve all tiles with workers. Doesn't really matter what you research but I recommend archery for sure and maybe even bronze working (Don't build any axemen or spears though!!!). Keep a few warriors fortified in Niwt-Rst. Build a settler and settle either on top of the Elephants to the south or just above it. Move all but 2 of your troops into the new city.
Send the Great Prophet you produce from Stonehenge to the second city.
Switch to Ethiopia when they spawn. City flips, gives you the prophet, use it for theology. Voila', you found Christianity and have bunches of troops now to wipe out Egypt and claim stonehenge for your own. You can use it to screw the Arabs out of Islam as well =)
Yes this is lame. Yes it works every time.
My friend got within 3 turns of Divine Right before the Arabs spawned by trading for Alphabet and building research in all of his cities ( I think he had 3, Aksum or Djbouti (which is spelled wrong in game btw), Moqdishu and one inland somewhere close by) without having a religion/prophet at all. So it might actually be able to be done without using prophets or attacking the Arabs before they found Mecca.
In my experience, even with the latest patch, Christianity is still being founded 300 years earlier than it should be (ie. 1 or 2 turns after Ethiopia spawns).
I know that "new modifiers" were added to help Ethiopia, whatever that means, I haven't noticed any difference myself though. Still seems like a ridiculously tough UHV to me and Ethiopia is horrendously underpowered compared to other civs in the era.