i switched from firefox to waterfox on my phone and have yet to spot any difference.
i heard some websites might have issues (e.g. web versions of office software) and some settings are missing but in my own everyday use i didn’t run into any of those yet.
i do not control mozilla leadership or their mishandling my data. the most influence i can exert as an individual is by not being a willing participant to their mischief. i’ll be happy to come back if the leadership changes and i get some guarantees.