A WebExtension for converting imperial units in inline text to the metric system
You can install it from Firefox Add-ons.
Alternatively, you can temporarily install it from the sources
for development purposes from about:debugging. From there, click on "Load temporary add-on" and select manifest.json.
The extension is not packed, it must be installed from chrome://extensions. Enable Developer Mode, click on
"Load unpacked extension…" and choose the folder the extension's code is in.