[docs] Clarify wording in Working with the Browser

I think the change in #3889 misinterpreted this slightly; this makes it clearer.

docs/08-working-with-the-browser.md

@@ -13,7 +13,7 @@ React provides powerful abstractions that free you from touching the DOM directl
 
 React is so fast because it never talks to the DOM directly. React maintains a fast in-memory representation of the DOM. `render()` methods return a *description* of the DOM, and React can diff this description with the in-memory representation to compute the fastest way to update the browser.
 
-Additionally, React implements a full synthetic event system such that all event objects are guaranteed to conform to the W3C spec despite browser quirks, and everything bubbles consistently and in a performant cross-browser way. You can even use some HTML5 events in IE8!
+Additionally, React implements a full synthetic event system such that all event objects are guaranteed to conform to the W3C spec despite browser quirks, and everything bubbles consistently and efficiently across browsers. You can even use some HTML5 events in IE8!
 
 Most of the time you should stay within React's "faked browser" world since it's more performant and easier to reason about. However, sometimes you simply need to access the underlying API, perhaps to work with a third-party library like a jQuery plugin. React provides escape hatches for you to use the underlying DOM API directly.