In a on the Office Web Apps blog, Microsoft listed its Internet Explorer 7 and 8 browser as well as Mozilla Firefox 3.5 on Windows, Mac and Linux, and Safari 4 on Mac, as the official supported browsers. Office Web Apps are Web-based versions of Microsoft's Word, PowerPoint, Excel and OneNote desktop applications.

Absent from that list are the Opera and Chrome browsers, which have significantly less market share than either Internet Explorer or Firefox but are still competitors in the global browser market.

Opera is the European-based browser company that was instrumental in the European Commission bringing an antitrust suit against Microsoft over the inclusion of Internet Explorer in Windows. The suit has caused Microsoft to pull Internet Explorer 8 out of Windows 7 in Europe and offer a choice of browsers in the OS.

Google, which makes Chrome, is one of Microsoft's main competitors, and recently unveiled a plan to build a desktop OS of the same name to compete with Windows. In fact, Microsoft's decision to put its Office productivity apps online is due to competition from Google Docs -- Google's Web-based office suite -- in the low end of the market for productivity applications.

Microsoft did say in the post, attributed to Gareth Howell, program manager for Office Web Apps, that people should try using the applications in other browsers besides the officially supported ones, and provide feedback to the company about how they work.