Sorry but that's just... delusional. Yes the moment Firefox would charge money and become a paid product 90% of people would switch over to Brave et al. The average internet user or even Firefox user does not now what Mozilla's business model even is because they're not terminally online.
A browser like Firefox if it wants to compete with Chrome and wants to have an impact on the internet needs to be free because the average internet user is willing to spend exactly zero dollars on software. If anyone could make more money charging for their software than not they'd already be doing it, unless you think they hate money.
Same goes for all the tirades about Mozilla's management. Again the average person has no clue about it, they don't read news about software company management. Firefox has been losing ground because Google owns half of all major sites on the internet and Android and ships as a default on tons of devices, it's that simple.