Yes, but that was application capabilities, not platform capabilities: back with Netscape Communicator there was no insanely-capable JavaScript features like We

Yes, but that was application capabilities, not platform capabilities: back with Netscape Communicator there was no insanely-capable JavaScript features like WebUSB, WebRTC, TypedArray buffers, and so on. This is what we're referring to when we say web-browsers are like operating-systems: because of the capabilities afforded to JavaScript programs, not because the browser is bundled with a built-in mail client (like Emacs...) or because of non-web-platform feature bloat like Seamonkey. --------- I imagine eventually Thunderbird will come back as a 100% JS application (no more XUL?) in a normal Firefox (or Chrome, or Edge, or Safari, but not iOS Safari, because reasons) window - making use of a hypothetical-but-easily-imaginable WebIMAP, WebPOP, or just after raw TCP sockets become a thing in JS: https://wicg.github.io/raw-sockets/docs/explainer.html https://wicg.github.io/raw-sockets/docs/explainer.html