Fibonacci in +!()[]script
7,576 chars

Firefox / Safari 9 (WebKit Nightly)

The main byte-saver is fill()

alert(Array(48).fill().reduce(falsefalse=&gt;falsefalse.unshift(falsefalse[1]+falsefalse[0]),falsefalse},[1,1]).reverse())


Most non-alphanumeric characters (especially ; and &gt;) are very expensive so I'm really trying to minimize their use.

Script

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Chrome (11,605)

Original:

; is very expensive.

alert(Array(48).join(0).split(0).reduce(function(falsefalse){return falsefalse.unshift(falsefalse[1]+falsefalse[0]),falsefalse},[1,1]).reverse())


Script: Pastebin.