Off the top of my head: Early this year I was looking for a new job. Many company job application sites (for software development no less) were incredibly broken on firefox. My doctor belongs to a group of physicians and their portal doesn’t work in firefox. A retirement fund from a former employer doesn’t work either.
They’re decent, but they are sandboxing some of the most complicated code in existence. Looking at browser CVE’s, improvements have been made in some areas, but browsers continue to be plagued by security problems with no reason to believe anything will change before the heat death of the universe. Couple that with much web ‘innovation’ being driven by the giant conflict-of-interest called Google and my response is…turn off javascript when possible and run your browser from a VM that doesn’t persist state when turned off. Even then, don’t use Chrome or Edge unless it’s absolutely unavoidable.