In FF if the object being iterated over is large enough it will trigger an expensive cycle collection with Test #1. Test #2 runs approximately 100 times faster on FF. The difference is marginal in Chrome. To see the difference in timing, I recommend loading up the debugger console to see exactly how many ms each run takes.

Testing the cheapest pattern for filtering an array of objects based on attribute.

Testing the cheapest pattern for finding an object in a collection of objects based on attribute.

String Concat vs JSON.stringify

Iterating over array of {key, fn} vs object of {[key]: fn}

compare between plain js and jQuery

Iterating over array of {key, fn} vs object of {[key]: fn}

Compare GCD