It works on 7.01 but here's how.. Rated 5 out of 5 stars
Many people have experienced trouble installing this app as Firefox updates and the app does not keep up with compatibility. What I found was that you need to use a work around.
Search the web for this file: 1-clickweather-188.8.131.52-fx.xpi
There are a number of sites that hold the file. Save it somewhere on your hard drive, then open Firefox "File" menu, "Open File" and open the downloaded file. The app will then install and work as you want. It works perfectly. If you don't see it, go to "View" "Toolbars" and make sure "add-on" toolbar is enabled. I installed this file from a user group link a few months ago and it has worked with every update of Firefox without reinstalling. I thank whoever did the hack.