Firefox runs 11% faster in XP than Windows 7; IE, Opera run slower

Since we began our periodic check of the relative performance of the rendering and JavaScript engines in Windows-based Web browsers, where we've seen them run about 14% faster on average now in Windows 7 RC than in Vista SP2, we've been asked...what about Windows XP? It certainly seems like the faster and more nimble platform of the three -- certainly all the netbook manufacturers seem to think so.

Today, we decided to find out the answer to that question for absolute certain. In a fresh round of tests with Windows XP Service Pack 3, running on the exact same physical platform we use to test our Vista and Win7 browsers (a quad-core, Intel Q6600-based machine with a 965 chipset on a Gigabyte motherboard), the answer was an absolute surprise...It actually depends on the browser brand.

Most Web browsers will run faster on Windows XP SP3 than on the two later editions, verifying what our eyes and our gut feeling had been telling us for quite some time. The average speed margin is 10% for XP SP3 over Win7 RC, and 28% over Vista. So if you've ever felt that software on Vista runs noticeably slower than on XP, now your suspicions are confirmed.

But Internet Explorer 8 runs ever so slightly slower on Windows XP than on Windows 7...about one percent slower. Our performance index gives IE8 a 2.24 in XP SP3 -- about 224% the performance of IE7 in Vista -- versus 2.26 in Windows 7. And for the historical record, IE8 runs 11% faster in XP than in Vista, on the same computer.

All the Mozilla Firefox browsers, both stable and developmental, run about 11% faster in Windows XP than in Windows 7, which is just about average. The most dangerous of the developmental builds, the private alpha of 3.6 Alpha 1 "Minefield," runs a little bit better in XP than the others -- 12% faster in XP than Win7.

The other major exception to the faster XP rule is Opera. Both the stable build and the latest public beta fared better in Windows 7 than in Windows XP -- the new Opera 10 beta posted an index score of 5.26 in XP versus 5.33 in Windows 7. The Win7 platform was generally faster in all areas -- no single heat stuck out as extraordinarily faster or surprisingly slower.
Today saw new public beta builds from both Google for Chrome 3 (with just a few days having passed since the previous one), and from Opera for version 10. The Chrome 3 beta turned up the gas significantly, scoring a 15.11 in our index on Windows 7. But XP is the platform it loves most, with a 16.20 index score there, 8% faster than Windows 7.

But whose browser reigns supreme? That, too, depends on the platform. Apple's Safari 4 is the ruler of the XP realm for certain, with a 16.80 index score there. But its Vista score falls all the way down to a 12.11, letting Google Chrome 3 take the lead on Vista and Windows 7.