Lightweight, informative, and ad-free! Rated 5 out of 5 stars
All the other weather-monitoring add-ons I've seen are pretty "heavy" -- WeatherBug has a big honking advertisement, etc.
ForecastFox is lightweight, provides useful information, and lacks any advertising with the in-browser interface (of course, when one goes to AccuWeather for more details, some advertising is displayed, but it's not nearly as obnoxious as the WeatherBug ads).
Two thumbs up!