What is Forecastfox? Get international weather updates (via AccuWeather.com) displayed right in Firefox with this highly customizable extension. Forecastfox features:

Vertical and horizontal displays
Select multiple “favorite” locations
Set your preferred units of measurement (Fahrenheit, Celcius, or custom)
Dozens of weather icon styles to choose from
Designate pages to hide the forecast bar
Select the number of days you want a weather forecast
Lots of fine detail settings like info on humidity, wind, precipitation, visibility & more

WebExtensions Limitations:

Forecast bar will not be displayed on some sites from mozilla.org and google.com
Forecast bar will not be displayed on sites that do not have pages, for example error 404 (page not found)
Forecast bar will not be displayed on internal Firefox and GoogleChrome pages, for example about:addons , about:config , chrome://extensions/ , chrome://settings/ , etc.
Forecast bar will not be displayed on the WebExtensions pages "moz-extension://...." , "chrome-extension://...."
Forecast bar may not be displayed correctly on some sites. In this case, report the problem on the forum

Sorry for the inconvenience and thanks for understanding! ============ You also can use Forecastfox (fix version) for Google Chrome: https://chrome.google.com/webstore/detail/forecastfox-fix-version/boljdehmejbffnfiiicckjhafabdepnd ============ -- forums mozillaZine: http://forums.mozillazine.org/viewtopic.php?t=2913287 forums mozilla-russia: https://forum.mozilla-russia.org/viewtopic.php?id=6652