Chrome is run by an ad company with a vested interest in your data and has been outspoken about banning adblockers in the past.
Firefox is a completely open source project run by a non-profit organisation who accepts donations to cover costs.
Other Chromium-based browsers can generally be fine but the overuse of chromium reinforces web standards that are hard to reproduce. A web browser is a fairly complex beast these days even for the best programmers. Just see XMPP for an example of where things could lead to.
While it’s true that Firefox receives some of those donations from Google for being the default search engine, they have no influence over decisions made by the Firefox team whatsoever. That’s the short version of it.
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