Long overdue.
It's worth going into why this is something that is worth doing and also why FB has historically not done it.
FB's position for a long time was that they would not remove material just because it was factually inaccurate, in other words they treated Holocaust denial as being essentially ignorance. There is a truly cringeworthy clip of Facebook spokesdrone and former UK deputy PM Nick Clegg in a documentary on Holocaust denial, unfortunately I cannot find it online, where he lays this out. The problem, as David Baddiel shows in that documentary is that this is not actually a disagreement on a matter of fact where one party is mistaken. There is no mistake and the people who push this stuff know it.
I've often noticed that the people who most vehemently believe that the Holocaust did not happen are the people who really want it to happen again. You're not going to find people who deny that it happened and are not also raging anti-Semites. Here's why: they know that it happened. They know that you know that it happened too. They enjoy the agitation and the pain they are inflicting. When they say that they are just "asking questions" and trying to "educate themselves" they are using the language of academic inquiry which they know we are culturally inclined to treasure and protect above almost all else as a sort of cloak.
The reason, for instance why Deborah Lipstadt, probably the world's foremost scholar on Holocaust denial has always refused to engage in any kind of debate is for precisely that reason. Now, at first, one might say: "aha, but surely we should never foreclose academic debate? What is she hiding that she won't even debate them?". However this is to mistake their games for genuine inquiry.
It should be noted that there actually are debates among historians about the Holocaust but these are not over whether it happened but over where it should be placed in terms of historical context - is part of genocide studies, a sui generis event, part of a long arc of European anti-Semitism? and over whether it was always part of a Nazi master plan or effectively emerged as a consequence of bureaucratic manoeuvring and favour-gaming by Nazi officials who wanted to rise through the party. These are often quite intense as well, with people having some very strong views. There is no such thing as a historical debate about whether the events themselves happened.
Sartre is still very relevant here: Never believe that anti-Semites are completely unaware of the absurdity of their replies. They know that their remarks are frivolous, open to challenge. But they are amusing themselves, for it is their adversary who is obliged to use words responsibly, since he believes in words. The anti-Semites have the right to play. They even like to play with discourse for, by giving ridiculous reasons, they discredit the seriousness of their interlocutors. They delight in acting in bad faith, since they seek not to persuade by sound argument but to intimidate and disconcert. If you press them too closely, they will abruptly fall silent, loftily indicating by some phrase that the time for argument is past.