I use a web application that lists items in a table, which provides a link to download the table as a CSV file. It used to work fine in previous versions of Firefox. However, in the current version, while the file save dialog defaults to a filename that ends in .csv and CSV is selected in the "Save as type:" drop-down, the data in the file that Firefox actually saves is in XML rather than CSV format. I don't know in which version of Firefox this behavior changed, as it's been a couple years since I tried to use this feature. Or I suppose it actually could be a new bug. I do know that when I use the same feature in Microsoft Edge, it saves the CSV file in the correct format, so this behavior seems to be peculiar to Firefox, rather than anything wrong with the web application.