>Facebook was going to compete with Google for some advertising sales but backed away from the plan after the companies cut a preferential deal, according to court documents.

>Facebook executives outlined the company’s options to Mark Zuckerberg...: hire hundreds more engineers and spend billions of dollars to compete against Google; exit the business; or do the deal.

It's one of many things FB and G did together. Even more are listed in the antitrust lawsuit against Google.

[1] https://www.nytimes.com/2021/01/17/technology/google-faceboo...