Hi alexismya, this looks to be a configuration issue on the server.

Some web servers do not know what content type to send for the newer Office formats such as xlsx and docx so they send "text/plain" which Firefox tries to display in a tab, or a generic binary file type, which forces a download. In this case, as shown in the attached screenshot, the server is sending "text/plain".

For the webmaster's reference:

This thread has the necessary file extension to content-type associations for Office OpenXML format documents:

http://stackoverflow.com/questions/4212861/what-is-a-correct-mime-type-for-docx-pptx-etc

For example, to send the content type "application/pdf" with files that have a .pdf file extension:

AddType application/pdf .pdf

I believe those lines can be entered in the server config file httpd.conf, but if permissions do not permit that, an .htaccess file often is used. Because it's easy to break a website with a change to any configuration file, the .htaccess file should be tested in a new folder that won't affect users of the live site.

That is a ZIP archive as you can see by the PK signature. You will have to save the files as a ZIP archive (.zip) and extract the files with an archive manager.

It's true that the Office Open XML formats (xlsx, docx, etc.) are zip archives, but Microsoft Office applications consume them in their compressed form rather than requiring that you decompress them first.