Really happy to have found an extension that uses the Dark Sky API. The developer has been fantastically responsive and has responded to any issues personally and quickly. You won't be disappointed.

I was using this on Chrome and was glad to see it on Firefox as well! Nice weather program with simple, clean interface. Tim is quick to respond to questions and problems and has been very helpful!

Just fyi, this needs geolocation to be on in order to work properly. So if you just get a spinning icon, make sure you haven't disabled geolocation in about:config. :)