personal.htm & personal.xls in Macro

I know that if I want my Macro or UDF to be available in all open workbooks,
I should save them in Personal.
But there are two personal in my Project-VBAProject tray one with .htm and
the other with .xls suffix.
What is the difference between them?
I am a novice in Macro and don't too much about it. Please explain in
beginners level.
TIA, Rasoul Khoshravan Azar

Rasoul Khoshravan Azar