I am trying to download a spreadsheet file which has a .xlsx extension. Firefox insists on downloading the file (my default action) but I want to be given the option to open in my spreadsheet program (Libreoffice). Looking in Settings and scrolling down to Files and Applications -> Applications, there are other spreadsheet formats present but not one for .xlsx. How do I add the "Always Ask" option for .xlsx files? Libreoffice is the default system application for opening these files.