Chrome is part of the Safari family. They use the same rendering engine. For the most part, you have the IEs and everything else. The "everything else" is standards compliant and should work fairly similarly. The IEs are noted for their unpredictability. Still, there are differences between the standards compliant browsers. They can be due to a slightly different interpretation of the standards, or they could be due to bugs. Rendering bugs are fairly rare in these browsers, though. But as I alluded to above, differences between standards compliant browsers are nothing compared to what IE does. Even different versions of IE can vary wildly. Also, the IEs have all those "modes" to pay attention to... standards mode, quirks mode, compatibility mode, etc. Note that standards compliant isn't necessarily "standards complete." CSS 3 is filtering in, for instance, but because it's not yet "official," different browsers have implemented different aspects of it. I guess if I were to look at a major project like you're doing, I'd test the IE family, the Mozilla family, the Safari family, and Opera.