By Agence France-Presse
The company said profit had climbed nine percent to $5.14 billion on revenue that leaped 33 percent to $13.7 billion in the quarter that ended September 30.
The number of people who used Facebook monthly rose 10 percent to 2.27 billion, but analysts had expected that figure to be slightly higher.
Facebook announced the results as it strives to fend off concerns about how well it protects the data of users and defends against use of the site to spread misinformation aimed at swaying elections.
Controversies that have battered Facebook since the 2016 presidential election in the US have even caused some to question whether co-founder Mark Zuckerberg should keep his post as chief executive.
"Our community and business continue to grow quickly, and now more than two billion people use at least one of our services every day," Zuckerberg said in the earnings release.
"We're building the best services for private messaging and stories, and there are huge opportunities ahead in video and commerce as well."
Facebook shares dove 5.4 percent to $138.33 in after-market trading, during an earnings call in which Zuckerberg said he expected 2019 to be "another year of significant investment" for Facebook and executives projected revenue growth to slow.
Facebook said it finished the quarter with 33,606 employees in a 45 increase percent over the number of workers it had the same time last year.
Just weeks ago, Facebook activated a "war room" as a nerve center to halt misinformation and manipulation of the largest social network by foreign actors trying to influence elections in the United States and elsewhere.
The war room at the company's Menlo Park headquarters in California is part of stepped up security that will be adding some 20,000 employees.
Last week, Facebook said it had taken down accounts linked to an Iranian effort to influence US and British politics with messages about charged topics such as immigration and race relations.
The social network identified 82 pages, groups and accounts that originated in Iran and violated policy on coordinated "inauthentic" behavior, Facebook head of cybersecurity policy Nathaniel Gleicher said.
Gleicher said there was overlap with accounts taken down earlier this year and linked to Iran state media, but the identity of the culprits had yet to be determined.
Spending on security and election-related defenses were likely part of the reason overall costs and expenses reported in the quarter rose 53 percent to $7.95 billion from $5.2 billion a year earlier.
In what could wind up costing Facebook more money, British finance minister Philip Hammond said he planned to introduce a digital services tax aimed at tech giants from 2020, responding to public outrage over low tax payments by US tech giants.
"It is only right that these global giants with profitable businesses in the UK pay their fair share," he told lawmakers on Monday in a move aimed at helping British businesses struggling against fierce online competition.