Waterfox is not a mainstream browser, therefore its fair to assume its users come to it in search of something that don't get in the major players. I'm assuming again, but I don't think is much of a leap, that those needs are privacy related and having control over the software you use. Not having a faceless company behind the software, like Google for Chrome, Microsoft with Edge or even Mozilla with Firefox is a draw for users. Now having said that reading that its been bought by a company, and one that does business in advertising no less can be quite jarring. Its like you shopping only in a mom and pop grocery for years that's out of the way and more expensive, but you do it to help local economy. Then one day you get there and and while you load up your cart the owners tells you they work under Walmart now. The very thing you tried to avoid. Of course such decision is in the waterfox dev, and he has the right to do as he pleases but is understandable that some people might have problem with the sale.