The Alexandria videos do show something, perhaps a searchlight; the Cairene sightings may also show something, but exactly what is debatable.
This may remind my longstanding readers of the wave of Marian appearances back in 2009, which I blogged on, complete with YouTube videos. As I commented then, if it's actually the Virgin Mary, it's above my pay grade, but if it's a sociological phenomenon produced by growing sectarian tension in the country, it's fair game for commentary. Coming just after the Maspero killings, and at a time of deepening societal tension in Egypt, one need not accept that this is miraculous to understand the popular reaction.
The Virgin Mary plays a special role in Coptic tradition, since the story of the Flight Into Egypt in the Gospel of Matthew tells us that the Holy Family visited Egypt while Jesus was an infant. Coptic tradition has inflated the few verses in Matthew into a detailed itinerary, complete with miraculous stories and visits to practically every Church along the Nile (and quite a few mosques). Because of the Holy Family stories, many Muslims also venerate these sites, since Mary plays a major role in Islamic tradition as well.
When the first major Marian appearances took place in Matariyya in 1968, near a site venerated as holy to Mary, there were as many Muslim witnesses as Christians. (See my link from 2009 above.) That 1968 was the year following the humiliating defeat in the Six-Day War of 1967 and the loss of Sinai may not be entirely coincidental. There were Marian apparitions reported in 2000, 2007, and a wave at Christmastime 2009, the first of the real YouTube era, but also an era of sectarian tension and growing political dissent. Those videos (at the link) looked like some sort of electrical arcing of electric lights in one case, and Saint Elmo's Fire in another, but perhaps I'm too skeptical.
Friday night's sightings occurred 12 days after the killing of Coptic demonstrators at Maspero, the worst sectarian violence in years. Tensions are high; signs in the sky will be interpreted accordingly.
Some of the varied readings of the phenomenon on Twitter, in English, Friday night:
Of the following video clips, in those where I can see much of anything at all, it looks clearly like a searchlight on the clouds, so the first comment above, from Alexandria by the place names mentioned, would seem somewhat credible.
"Very very urgent: Appearance of the Virgin in the skies of Shubra [populous, heavily Christian part of Cairo] yesterday." I can't see much here, to tell the truth.
"Appearance of the Virgin Mary above the Church of St. Maximus and Bishop Musa al-Aswad in Alexandria": This, I think, is consistent with a searchlight on the clouds.
And this time, "Appearance of the Virgin Mary and the Archangel Michael Above the Clouds." I admire the specificity, though I only see one light, and I think it's a searchlight.