it was good when it worked, but now it only says

"Firefox Can’t Open This Page

To protect your security, keepa.com will not allow Firefox to display the page if another site has embedded it. To see this page, you need to open it in a new window."

but opening Keepa's frame in a new window doesn't load, so it's useless on Firefox now!

edit: The Camelizer - Price Tracker still works on FIrefox, but it requires you manually click it to see the price, compared to how Keepa used to automatically show it on the main product page (back when it worked.)