Useful, but needs work. Rated 4 out of 5 stars
This is a very useful little addon. It's not without serious problems though. I imagine this is still in its infancy, but I don't know that for sure.
The first and foremost problem is the tedious setup. There are no decent shopping categories. Granted you can create your own, but it's a VERY slow and drawn out process.
It should come with a standard shopping list category setup (dairy, poultry, fish, beef, paper goods, canned goods, cleaning supplies, salad dressings, sauces.... you get the idea), but it does not. When creating your own, it does not auto sort them alphabetically either.
Now that could be a good thing because you can place them wherever you wish (in order of your grocer's aisles if you will), but you cannot drag them into their proper place.
If you get specific with your categories, be prepared to spend well over a hour just to set them up. You have to scroll down, down, down, down, down, click the up/down button, wait for it to reload, then repeat until you manage to get it in place. This is for each and every one! There just HAS to be an easier way.
Now whatever you do, do NOT make the mistake of organizing your categories and NOT assigning an item to it. If you do, BEWARE. All your categories not associated with an item will be lost when you close Firefox. There is no option, as far as I can tell, to save unused categories.
All that aside though, if you're willing and able to take the time to organize it properly, it's a nifty little gadget. I'd prefer to have it as a separate app, but I'm happy to have it anyway.