Microsoft Office web apps won't officially support Chrome, Opera browsers
In other words, if you use Google Chrome, Opera, or another web browser, you may be out of luck. It's worth pointing out that Microsoft hasn't said that other browsers won't work. It's just that the company isn't going to take the time to support additional browsers.
According to the blog post, the Office Web apps will be designed to work without any plugins installed, but Microsoft recommends installing Silverlight, which will help the web apps load faster and perform better. The text will also be easier to read, and PowerPoint animations will be smoother with Silverlight installed.