how to automatically "Save " a page after certain intervals without clicking "Save Page As..."

[subhadip]

Hi,
I want to save a web page automatically in my local memory
after certain interval . Suppose
I have opened my yahoo mail account in firefox . I want to save the
opened page again and again
after certain interval in my hard disk( i will refresh the page in the
mean time using javascript) without any mouse click . I will
overwrite the file again and again . I will supply the current url of
my current session . Can you help me by giving hints or any code for
this automatic "save page as..."?
Regards