Does the end user of my application need to install browser extensions?

If you have integrated your application with Whatfix using the JavaScript embed method, your end users do not require any browser extension.
Your end users only need the browser extension if they don't have the access to the application code and cannot use the Javascript embed method of integration. When your end users require a browser extension, it's usually an internal use case and the deployment of the extension is done en masse as part of an IT policy.