Everything Metric Auto Unit Converter is a free Firefox add-on designed to facilitate seamless unit conversion from American units to the International System of Units (SI/Metric). This tool automatically appends the converted metric units in brackets next to the original units on various websites, making it particularly useful for activities such as online shopping or cooking. Users can expect conversions for length (e.g., feet to meters), weight (e.g., pounds to kilograms), volume (e.g., gallons to liters), and speed (e.g., mph to km/h). The add-on also handles area and volume conversions, ensuring comprehensive coverage of common measurement types.

The add-on features a convenient toolbar button that allows users to toggle the conversion on or off globally. Additionally, users can utilize a keyboard shortcut (Alt+M) to trigger conversions on demand, even when the extension is not actively running. The options page provides further customization, and the add-on requires permissions to read page data and store settings for optimal functionality. With its user-friendly interface and practical features, Everything Metric Auto Unit Converter enhances the web browsing experience for users needing metric conversions.