"Clearly this problem is not going away; I'm not even sure it's trending in the right direction", Burr said of the threat to U.S. elections from foreign influence operations on social media platforms.
"The actions we've taken in response. show our determination to do everything we can to stop this kind of interference from happening", Sandberg said.
Google too was to be present at this hearing, but the company did not send a senior executive.
Facebook Chief Operating Officer Sheryl Sandberg acknowledged to the Senate Intelligence Committee that the company was too slow to respond to Russian efforts to interfere in the 2016 US election and general American political discourse, but insisted it is doing better.
Dorsey offered an explanation of how San Francisco-based Twitter uses "behavioral signals", such as the way accounts interact and behave on the service.
This will be the first time Sandberg has publicly faced significant questioning about Facebook's role in the 2016 election.
Dorsey will appear before the US House of Representatives' Energy and Commerce Committee after Republicans raised concerns about how the social media platform polices content.
President Donald Trump used Twitter on July 26 to fault the website, without evidence, for using so-called shadow banning, or limiting the visibility of, prominent Republicans. Google, however, risks having an empty chair at the hearing after cofounder Larry Page declined to appear. Richard Burr, R-N.C., said Google doesn't "understand the problem" if it doesn't want to work with the government to find solutions.
Sandberg, in her prepared remarks, detailed how Facebook was addressing the problem but reiterated that the company was slow to spot it. Lawyers for Facebook, Google and Twitter were grilled by senators over the course of two days last October, after the extent of the Russian social media influence operation was revealed. Earlier this year, special counsel Robert Mueller indicted 13 Russians behind the social media effort.
On bias, the Twitter CEO said in prepared testimony before his second hearing that "Twitter does not use political ideology to make any decisions, whether related to ranking content on our service or how we enforce our rules".