FirefoxOS was eventually forked into KaiOS, which was the second most common mobile OS in India for a while, selling millions of phones.
It was never going to beat iOS, but it could've had Google's (and at the time Microsoft's lunch) for cheaper phones.
On the browser front, Google only had a third of the market at that point. Firefox was losing users, but the situation wasn't nearly as dire as it is right now.
And what would having millions of cheap phones meant for Mozilla? Not much if you ask me. Basically just Indian and Chinese ultra cheap phones that pay very little back and do little development.
Chrome might have only had a third of the market, but anybody around at the time could see that this was only a matter of time. Chrome was just better in so many ways. Mozilla needed to buckle down and focus all their engineer on the browser.
It was never going to beat iOS, but it could've had Google's (and at the time Microsoft's lunch) for cheaper phones.
On the browser front, Google only had a third of the market at that point. Firefox was losing users, but the situation wasn't nearly as dire as it is right now.