Firefox is now owned by ads company. By default there are enabled telemetrics and moreover companies starts to ignore compability of their web services with browser which market share is lower than 2% even goverments stops considering that browser. Mozzila instead of optimization of their browser spend time introduceing features like AI. I was trying to like that browser but mozzila effectively does not allow me. Now btw. I use just vivaldi. I know this is not fully open source.
They are not independent. It all soft fork. Everything depends on firefox. If firefox die all the forks will die with too.