How to detect browser addons in Firefox, Opera and IE?

How to - using either JavaScript or PHP - detect addons that are used by a user? In particular the ORB开发者_JAVA技巧IT addon.

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I realize this is an old question but it popped up on a google search for me. It most definitely is possible to detect browser addons. Here are a couple of resources to check out:

http://ha.ckers.org/blog/20060823/detecting-firefox-extentions/

http://webdevwonders.com/detecting-firefox-add-ons/

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In general, you can't.

Some addons (eg, Firebug) expose a client-side object model to the page, in which case you can detect them using Javascript.