Love this app! It's like being able to put a limit-order on an amazon item. Getting a message when the price drops below a threshold is awesome. I sometimes buy an item 6+ months after I originally see and mark it on camelizer.
For those complaining about incompatibility, I have been through every update of FF for the last 1.5 years, and am currently on FF 58.0.2, and have successfully used this extension -- alongside ublock origin, print edit, video download helper, user agent switcher, and with and without flash or java.