Hello,
As I said, it must not be problem of your code as you can do it with IE.
Did you clear cache before making any new request on FF?
1. Clear cache, close and open FF again.
2. You may debug, add breakpoint on page2 to see what Session contains.
3. Use 'True' in response.redirect method, this will stop execution of current page.
Kindly try this and let me know.