Full page screenshots don't work with all pages Rated 3 out of 5 stars
It does work with some pages (including e.g. this one) but fails on others and then it only saves the visible portion. (No, I'm not talking about dynamically loading pages like the FB news feed.)
Might be related to some rendering optimization in the browser, may have worked earlier, but as of now it's unreliable. Actually it does the same as the screenshot node in the developer tools, so doesn't have too much added value for the occasional user.
Doesn't do full page screenshots Rated 1 out of 5 stars
That's it. Despite what it advertises, it will only screenshot the visible area (yes, even when you select the full page option from the menu). As that can be achieved in other ways and as this was exactly the reason I've installed this, I'm giving it a 1-star.
May have worked on earlier versions of FF, but if it's not possible anymore, the description should be updated or the incompatibility noted somehow.