In one example, the memo said Facebook took nine months to act on a campaign using "inauthentic assets" to boost efforts by Honduran President Juan Orlando Hernandez to mislead people in that country.
The more than 6,000-word memo cited organized efforts to harass, mislead or manipulate people in Azerbaijan, Ukraine, Bolivia, Ecuador, India and elsewhere, along with election manipulation efforts in the United States and Brazil.
The document offers new insights into the efforts around the world to manipulate content on the world's biggest social network, and Facebook's struggles to thwart them.
In response to the memo, Facebook said it has been stepping up its efforts to stop disinformation and manipulation.
"We've built specialized teams, working with leading experts, to stop bad actors from abusing our systems, resulting in the removal of more than 100 networks for coordinated inauthentic behavior," Facebook said in a statement to AFP.
"It's highly involved work that these teams do as their full-time remit. Working against coordinated inauthentic behavior is our priority, but we're also addressing the problems of spam and fake engagement. We investigate each issue carefully, including those that Ms. Zhang raises, before we take action or go out and make claims publicly as a company."
BuzzFeed said it did not publish the full memo because it contains personal information.
Zhang declined to be interviewed, according to BuzzFeed, which said she turned down a severance payment from Facebook that would have contained a "non-disparagement" requirement.
She wrote in her post that she did not want details of the memo to be public for fear of disrupting Facebook's efforts to protect the 2020 US presidential election.
"The last thing I want to do is distract from our efforts for the upcoming US elections, yet I know this post will likely do so internally," she wrote.