A browser extension is a small software program that adds features to a web browser such as Chrome, Firefox, Edge or Brave. Extensions are installed from an official store and can read or change web pages, add buttons and store data. In crypto, the most important extensions are Web3 wallets such as MetaMask, which hold private keys and let users connect to decentralized applications and sign transactions directly from the browser. Extensions can also be dangerous: fake wallet extensions, malicious updates and add-ons with broad permissions have been used to steal seed phrases and funds. Users should install only from official sources, check the publisher and keep the number of extensions low. Also see Hot Wallet.