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Opera is obviously not content with sitting on the sidelines when it comes to being the fastest browser out there. Back in February Mozilla decided that it was time to optimize it’s JavaScript performance, and used a technique called Profile-Guided Optimization (PGO) that gave it a nice boost. Opera decided to jump on the PGO bandwagon as well with this week’s release of Opera 9.5, and here is their explanation of how it works:

With this technique, Opera is compiled twice. The first compilation creates a specially instrumented build that gathers statistics about which code is called and which variables are used most often. The instrumented build loads sites automatically using “URL player”, a testing feature available in every Opera build (more information about that in a later blog post). This information is dumped into files and used to produce the final build that’s optimized based on the gathered statistics.

Did it help? Unfortunately there are some bugs in Opera 9.5 that prevent it from finishing the Sunspider test, but in the areas it does complete the result is normally better than Firefox 3 Beta 5. It does, however, consistently beat Firefox 3 in the MooTools SlickSpeed test in addition to this JavaScript benchmarking tool.

Congrats Opera! It looks as though you might be recapturing the JavaScript performance crown, but we’ll have to wait and see what the final version of each browser is like before we make any conclusions along those lines.

Be sure to checkout our more complete article where we compare the performance of more browsers.