PDF and Microsoft Office file preview is not working with IE9

Bug Description

1. Access Confluence using Internet Explorer 9, a supported browser of Confluence 5.7
2. Upload a pdf file into a page
3. Create a link to the recently attached pdf file
4. Save the page
5. Click the pdf file link created

Expected behaviour

Confluence should be able to preview the file successfully in IE 9 as it is a supported platform and pdf file is one of the priviewable files.

Result

Confluence unable to preview the file with the warning message as describe in the screenshot below:

Workaround

• Viewfile pdf is still working in IE9.
• In order to open the link without downloading the file, user can use "Open in New Tab" option.
• Disable Confluence Previews plugin (PDF will be viewed as prior to Confluence version 5.7)