Hi,
I'm Kishan. Please have a look at my profile and reviews to know more about me.
I've gone through your project description and I understand that you want to detect if a particular add-on had is installed in the browser.
But each add-on has to be detected in a different way. For example, Alexa Toolbar is detected by the user-agent string and Ablock and similar add-ons are detected by checking if ads are visible.
Can you please tell me which add-on and which browsers you are interested in? I can then tell you if it's possible, and how much time I'll need to finish it.
After that, I can provide you a small demo or mockup before we start.
Regards,
Kishan