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Mozilla can't save Firefox. It's not that Firefox can't be saved, but rather that Mozilla as an organization is not capable of doing so.
My take is this - Despite a history of being relatively privacy friendly, the vast majority of funding for the organization comes directly from Google (To the tune of ~90% of their total funding, straight from Google so that Google can maintain its position as the default search in Firefox).
That leads to insurmountable conflicts of interest - They claim they are for people and for privacy, but they are funded almost entirely by Google, and have to secure search deals for their continued existence (the latest just this year: https://www.pcmag.com/news/mozilla-signs-lucrative-3-year-go...).
In this light - I believe it actually BENEFITS mozilla to keep Firefox relevant, but not good enough to replace Chrome. If the browser genuinely becomes good enough that customers start switching from Chrome to Firefox en mass, Mozilla needs a replacement funding plan because Google can essentially turn the lights off at any point by simply refusing to pay them for search at next contract renewal.
While they've dipped their toes into paid products... most of them are not particularly relevant or compelling on their own merits (that's not to say they're bad, just not all that innovative or likely to drive enough revenue to replace the 500million a year google is paying them)
So not only do I not believe that Mozilla is capable of "saving" Firefox in this way, I don't believe they have the right incentives to even seriously try.