Forecastfox Weather is a great add-on for Firefox.
"Get international weather forecasts from AccuWeather.com and display them in any toolbar or statusbar with this highly customizable and unobtrusive extension."Using your cursor to hover over the various icons in Firefox's status bar, activates information pop-ups.
You can set your location, dictate the number of forecast days, and configure the add-on to display information in the units of your choice. Excellent!