I don't know about this. Almost every thread about Firefox has someone recommending Brave. Firefox is solving a problem users don't know they will miss until it's gone: browser consolidation. The problems that needs solving now are privacy related and Mozilla's absolutely poor management of Firefox on this front causes others to look for other solutions.
Firefox should be the most privacy centric browser available. However it doesn't seem like management gets the memo. For example, not too far in the past, they made news for putting ads in the search bar and providing a config option (in about:config) to even allow personalization. This kind of thing just destroys the brand and trust with users. If someone asked me to rank browsers based on privacy, I don't think I could give you a rank order, other than the fact that Chrome (and I'm assuming IE) would be near the bottom.