While it is true that most things that get used have people with grievances, using that as an argument to dismiss complaints is not productive.
> Plus for Firefox to grow in popularity/stay relevant you need people to care
Yes, and people care more when the browser developers care about them. Mozilla is intent on showing that only their design vision matters and customizability will go as soon as it slightly inconveniences them.
> and you need the browser to improve
But not all changes are an improvement.
Plus for Firefox to grow in popularity/stay relevant you need people to care, and you need the browser to improve. Complaining is better than silence in that context.