Forecastfox (fix version) v4.26 
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
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You also can use Forecastfox (fix version) for Google Chrome:
https://chrome.google.com/webstore/detail/forecastfox-fix-version/boljdehmejbffnfiiicckjhafabdepnd
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forums mozillaZine:
http://forums.mozillazine.org/viewtopic.php?t=2913287
forums mozilla-russia:
https://forum.mozilla-russia.org/viewtopic.php?id=6652