I am sending a csv and xlsx file through stream to user for file download. While user can save and access both format files in all browsers, in FireFox, if user opens .csv file, MS Excel tries to open it which is mapped as default application for csv format. But MS Excel gives error of invalid file format and weird aspect is that now format of the file is filename.csv.xlsx, while the original file name is filename.csv which is also displayed in download option box of FireFox.
The file format still is filename.csv if we save it through any browser including FireFox and MS Excel is successfully displaying content when saved and opened or even direct open through IE.
It seems MS Excel is changing file format prior to opening file when accessed through FireFox. Is there any way to remove this inconsistency. PFB relevent details: