With new ff I could make it work only along with "The addon bar (restored)" plugin, that adds the addon bar back to the browser. At the same time it is not always easy to use, it simply turns itself off, sometimes i have to click on it's button many times to keep it open for more than a second.
It does not seem to do anything useful in the latest firefox, and since there also does not seem to be neither documentation nor examples it was not very helpful to me. Tried some XPath I wanted to check and could not discover any sort of responsiveness. So I immediately deinstalled it again and went for FirePath.
The tool is great to start with. The way it just seamlessly fits into my browser makes it easier to try on...I don't have to navigate out of the page I am testing...
But the addon hangs after using it continously for sometime. Then the xpath input textbox isn't visible but then the elements are still highlighted. After feeling helpless to stop the addon, I had to repeatedly restart the browser to restart the addon.