SelectON is a Firefox extension designed to streamline text selection and enhance user interaction with web content. This tool allows users to copy or search any text with a single click, similar to functionalities found in Opera browser. It includes a currency converter that supports over 30 currencies and more than 10 cryptocurrencies, as well as a basic units converter for metric and imperial measurements. Additionally, it features contextual buttons that adapt based on the selected text, offering options like 'Open link', 'Translate', and 'Show on map'.

The extension boasts a smart selection feature that ensures accurate text selection without losing characters, coupled with customizable tooltip appearances and selection colors. Users can enjoy live translations, quick access to dictionary definitions from Wikipedia, and the ability to highlight text. SelectON emphasizes user privacy by not collecting personal data and maintains its open-source status for transparency.