Google Chrome OS users were already enjoying build-in browser extension to open Microsoft Office documents. Now, even Windows and Mac users can install Chrome extension and can open Microsoft Office documents in Google Chrome browser.
Open Microsoft Office documents on Google Chrome

Office Viewer beta version of Google Chrome as an extension can be installed in Chrome 27 or later versions, the extension is currently only available in Beta version. If you want to use a pre-release version, you can install from the Chrome Web store

The majority of the MS Office extensions can using this chrome plugin, including .Doc, .Docx, .Xls, .Xlsx, .Ppt, .Pptx. Office Viewer interface is very similar to Chrome’s PDF preview interface, it comes from Quick Office since Google acquired Quick Office last year.

The plugin is still in Beta version and has many bug and imperfections. For example, while testing we found that it can not open the simple spreadsheet. In another test .Docx files sometime work and most of the time it converts the file into picture.

On the plus side, Opening an office document in dedicated sandbox would protect you from any document infected from virus or malware.

However, I think it is not a prime time to launch a buggy beta version but still it is a necessary plug-in. Beside chrome extension you can use Google Drive to browse the file, you can also use Zoho Docs to open Office files online.