I insisted on Firefox for a while because Google hegemony but in the end I switched to brave.
1. Firefox often loses settings
2. Also it is really, really bad at saving your session. After losing important tabs I ignited that but...
3. After painstakingly preparing a bunch of docked tabs, it lost these too.
4. Frequent interface changes, often for the worse (to be honest my favourite interface was firefox 2.0)
5. It often breaks extensions too, this is felt heavily on Thunderbird where I have to often teach my family all over again how to do what they want or have to code more extensions myself because some critical extension does not work anymore.