I know there is a similar question but this is different and I did NOT get an answer from that question.. Anyways here goes..

I use the addon auto-refresher on firefox and recently got a message from a website mod telling me that they know I am using it. They say they know each and every user that is using this mod. Are they really able to do that or are they just guessing? I actually feel a bit violated knowing that they are able to see which addons I am using and operating. I know the other question said that they cant but these people are claiming they have and know each user that is using it. I just want to know if they really can figure that out..and how.

Also, maybe it's just the auto-refresh addon they are able to detect? If so why?

Thank you so much for answers in advance!

  • 1
    Because it's refreshing at a very regular interval. – Tyson Sep 9 '14 at 1:57
  • They may not be able to know which addon you're using, but they can see patterns in your refreshiing which lead them to conclude you're using and automated tool to do it. – heavyd Sep 9 '14 at 2:08

As others have said, purely client side plugins like yours can be detected via frequency analysis, so no additional information is required.

For server-interactive plugins and extensions, the list of installed/active browser plugins is available to websites as part of your agent information. This is not just true of Firefox, but of every major browser. See here for info from Mozilla on how sites can ask firefox to enumerate all its plugins, or to find a specific one.

This list is how sites can tell you need to install Flash, or update the version of your plugin. same with java.

you can use this site from the Electronic Frontier Foundation, to discover what information your browser leaks, and determine how identifiable it makes you. when you look at user agent info closely enough, most users are pretty easy to identify, even if their IP address changes.


you can also check out BrowserSpy, to query info from your browser by catagory.

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  • Is Auto-refresher a plugin or an addon? Also, from what I understand is that they cant know 100% that I am using that addon but only assume that I am because of the refreshing intervals? – JJ Marie Sep 9 '14 at 2:30
  • Plugin/add-ons should have equivalent meaning for these purposes (e.g. a 3rd party piece of code that operates to extend functionality of the browser). That said, there is a subtle difference -- forums.mozillazine.org/viewtopic.php?f=8&t=2121149. The refresher would an "extension" in Firefox. "Plug-ins" like Adobe Flash, etc. are easily detectable. Regarding anything that can't be directly tested for, 100% assurance doesn't mean total ignorance. If I watch your house for a week and you leave between 7am-8am and return home between 5-6pm, I have a pretty good idea of your work schedule. – Anaksunaman Sep 9 '14 at 3:21
  • @JJMarie, if you are referring to this product, then yes, it is a addon. addons.mozilla.org/en-US/firefox/addon/auto-refresh it can be detected by the site by including javascript like that described here: developer.mozilla.org/en-US/docs/Web/API/… – Frank Thomas Sep 9 '14 at 4:32

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