Browser Extensions in 2024

I'm reading back through Rob Walling's Stair Step Method and it seems like step 1 is primarily aimed at making apps for bigger SaaS ecosystems like Salesforce, Zoom, Slack etc

Most of these are platforms I don't use regularly, so I wouldn't know what users might want, but I am in my web browser constantly.

Is building a browser extension as a Step 1 Project viable today?