They didn't replace affiliate links. They had a feature similar to Firefox Suggest or whatever's in Chrome/Edge nowadays I think. They had a deal with eg. Binance, and if you typed Binance in the address bar, their Binance promo would show up as one of the results.

They had a bug in it where if you typed a valid URL (eg. binance.us) it'd still give the sponsored link as an autocomplete which it shouldn't have. That bug stood for one day, if memory serves, and the feature was turned off by default.