It sounds like you are using the plug-in in a private window without approving the plug-in to work in private windows. Firefox recently started requiring that each plug-in be authorized to work in private windows. Go to your Add-Ons page in Firefox, click the 3 dots on the right of the add-on name, select More Options from the menu that appears, then click Allow next to "Run in Private Windows".

This extension does not claim to block ads -- it blocks access to known porn and malware domains, nothing more or less. If the ads are being served from a legitimate domain, you are faulting it for something it was not designed to do. What you need is an adblocker. I recommend uBlock Origin.

If you can be more specific about what did not work for you, I'd be happy to help you work through it. There are over 5000 weekly users of this plug-in, so something must have gone wrong in your setup. Yours is literally the first bad review it's ever gotten.