> I just worry that people using some of these alternative browsers are opening themselves up to security issues since those code bases are less well-tested for security problems
Absolutely. The web browser is one of the most notorious attack vectors on computers these days. I find it hilarious that a vocal minority of power users is protesting this _massively impressive_ Firefox release just because they lost Tree Style Tabs or some extensions for downloading videos. Switching to a legacy fork like Waterfox or Firefox 52 ESR is not an enlightened move!
I just worry that people using some of these alternative browsers are opening themselves up to security issues since those code bases are less well-tested for security problems, and often they don't have the developer resources to implement things like process isolation and sandboxing.