It's good to see browsers picking the good features of each other & in some cases refining them so that it becomes a standard in subsequent versions of other browsers. Tabbed browsing, In-line Search, "Find As You Type", Undo Close Window (Ctrl+Shift+T), built-in Developer Tools are all innovative features started by one browser brand & supported by the rest.
An interesting new feature that has come up in Firefox, Safari & Chrome that I'm really finding useful is Spell-Check. Every time there is a typo or a spelling mistake in a text area within a web page that you are typing into, the red squiggles show up when you commit a spelling mistake & you can pick up the correct spelling from the context menu. Safari 4 also introduces Grammar Check, although it's not as refined as we see in MS Word. I hope Spelling & Grammar Check go on to become a standard browser feature.
Also see:
Keyboard shortcuts common to Firefox & IE 8
The Collective Decisions of Competitors