What Function or Feature Should a Browser Support?

In another topic about browsers, one member said concerning their browser of choice, "Speed isn't really an issue. Instead, it's more about the browser's features." I thought that was an extremely interesting point, so rather than drive that thread [further] off-topic, I decided to start this thread, with a comment, and a couple questions, and ask that you add your own comments as to what you expect a browser, your next browser, to do or support.

One necessary ground rule - this is not about which browser is better or not, just what you feel your next browser should do, or support. Features you like, must have, or would like to see. Or even features you don't like.

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A word processor should enable a user to create documents. An anti-malware scanner should detect and protect you from malware. A firewall should protect ports. An operating system should make all of them, and all your hardware work seamlessly together.

History has shown us over and over again that when software makers start adding extra features and functions (some may say, "flashy lights" or "bells and whistles" - some may say, "bloat" or "foistware") to applications, anti-malware programs, firewalls, operating systems, etc., that our computers (hard drives, desktops, Start menus, and system resources - RAM and CPU clock cycles) and patience often tend to get bogged down with all that extra "fluff". With that in mind,

What basic "function" or functions do you expect your browser to perform?
What native (integrated) "features" must your browser include?
What "add-on feature" or "plug-in" is a "must have" for you? Should it be native to all browsers?