Toffee is currently in Developer Preview. Follow these steps to install the unpacked extension directly into Chrome or Edge.
Since you are running Toffee locally, you need to build the extension first. Open your terminal in the Toffee project directory and run:
Open your browser's extension management page. For Chrome, go to chrome://extensions/. Toggle Developer mode on in the top right corner.
Click the Load unpacked button that appears. Select the packages/extension/dist folder from your Toffee project directory. The Toffee icon will appear in your toolbar!