Here’s a six-minute YouTube video explaining how to use it
TL;DW: Click on the extension icon, use the drop-down lists to find a browser and OS, select a pre-configured user-agent string from the list, and click “apply (container)” or “apply (all windows)”. Having your user-agent string change randomly with each request is possible but requires writing a bit of JSON in the options.
I put a Kbin and Lemmy community in the sidebar of /r/vexillology shortly after the beginning of the API protest.