You won't need an extension to add a cryptocurrency wallet to your browser. Brave has updated its desktop browser with a built-in crypto wallet (appropriately, Brave Wallet) that lets you buy, sell and swap with "almost any" asset. While this won't always be more convenient, Brave claims the included wallet should carry fewer security risks and performance penalties than the usual browser add-ons.
This is a self-custody wallet that still allows use of other wallets (such as Brave's legacy Crypto Wallets) and ties into hardware wallets from the likes of Trezor and Ledger. You can track crypto market data, find the best price matches and control portfolios that include NFTs. It supports EVM-compatible blockchains and is both open sourced and open licensed.
The wallet is available through the settings page in Brave 1.32. It's coming to Brave's mobile browsers "soon," the company said, and the Solana blockchain will become the default for decentralized app support in 2022. You probably won't download a browser just for native crypto support, but this and Brave's usual privacy-minded features might tip the balance if you're looking for an alternative to mainstream web clients.