It used to work fairly well for me, but recently it has stopped and doesn't find anything at all. On many sites such as google search, it very rarely even show the toolbar. When it does show the toolbar saying it is searching for cheaper prices, it never finds any.
I think that this has only occurred since I updated to the latest version 3.1.5.
I installed the latest version in both Cyberfox 52.9.1, Waterfox 56.2.12 and Firefox 65.01 to try it out and it still does not find any relevant results. The best it came up with for product searches were USA $ results and that was after setting the preference to United Kingdom. After 8 years since my first review, it still does not work!! Utterly useless IMO.