Is there a way to see what firefox addons someone has on their browser

I believe someone is using a firefox add on to edit post vars midstream. is there anyway i can check to see if someone is using what addon?

 

I'm not sure if you can but either way, this might be an invasion of privacy.

 

You mention both post vars and plugins. With post vars, I can build a form with whatever post vars and submitted to your URL so I am not sure how you would control that by checking plugins.

You can detect plugins through JavaScript. Commonly, it's done to check Flash or Java version. What sort of plugin were you looking to check?

 

I don't think this is possible with a program, but as tbarr60 said, you can detect plugins through JS.