I'd rephrase it. Browser is turned into a virtual operating system for millions of people already. While it can be useful, I don't really like when that trend is pushed to the extreme and everyone rushes to run everything through the browser even without clear benefits. The point of that? I always prefer standalone chat clients (as well as e-mail clients and etc.). If some chat service can't interoperate with standalone clients, it's garbage.
Facebook can by the way, since they do use XMPP. Their problem is unwillingness to support federation. They are too selfish. So I never use their service (nor do I use their social network anyway).