Download the 419-page PDF file containing 16,000+ links (updated in May 2020) to genealogy & history Facebook groups/pages (in English) here: “Genealogy on Facebook” List
There is a clickable table of contents at the beginning of the list, starting with U.S. states & territories in the first section, other countries in the second section, and various categories in the third section (adoption, African American, Jewish, surnames, etc.). Clicking an entry in the table of contents will take you directly to that category within the list, and clicking a link will take you directly to that Facebook page/group.
To be notified each time the list is updated, please “like” my professional Facebook page at www.facebook.com/SocialMediaGenealogy.org.
Gail Dever has a broader Canadian list that includes French-speaking groups & pages that can be downloaded at Facebook for Canadian Genealogy, and Alona Tester has an Australian list that can be downloaded at Facebook for Australian History & Genealogy.