We are serving files with the .xlsx (excel 2007/2010) extension. IE, Chrome, Safari all download the file and open excel just fine.
For some reason Firefox is appending .xls to the extension. I found this: https://support.mozilla.com/bs/questions/758363
However, the instructions weren't very specific and completely unclear to me.
How can I tell Firefox not to screw with the file extension?
I'm using 3.6.13 on Windows 7.