Chrome and Firefox devtools are very very behind in modern debug features, it’s like programming in the early 90s again! Not just that, but debugging is also extremely fragile, crashing often on small programs for no good reason. It can’t even call tostring automatically in the watch windows because JavaScript VMs have no easy way of quickly sandboxing those fine grained calls.
I'm not sure I understood the toString() issue you described here, and I don't recall encounting crashes with any particular regularity. What I do recall is having to deal with VS2017's inability to execute or watch many LINQ/lambda expressions which made certain debug sessions completely useless.
The biggest issues I've had with web browser debuggers is the interaction(or lack thereof) between source maps and debugging. I don't know any of the modern debug features that the browsers are missing - could you mention some?
