Yeah. The way it works with Lemmy is that communities are federated one-by-one with an instance, rather than whole instances federating with other instances.
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 would say a user agent spoofer would be more useful for this particular image. The Mozilla team recommends User-Agent Switcher and Manager for Firefox users.
Ting Tang Wallawalla Bingbang