Google's Closure Tools were used to create Gmail, Google Docs, and Google Maps, among other applications.
The Closure Compiler can be run as a command-line tool, a Web application or a Firefox extension.
Google has focused on speed across its Web applications and has made speed a major goal for its Chrome browser. Speed, for Google, is a competitive advantage.
In a browser comparison conducted on a Mac Pro (dual 2.8 Ghz Quad-core Intel Xeon), between the developer version of Chrome (220.127.116.11), Firefox 3.5.4, and Safari 4.0.3 (6531.9), the v5 benchmark scores -- higher is better -- were Chrome (4465), Safari (2761), and Firefox (365).
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