How Browser Extensions Can Mess Up A Captcha & What To Do About It

Simon Slangen 18-06-2012

captcha problemsThe ‘captcha failed’ notification is constantly lurking in the shadows. At times, it’s almost as if some dark, twisted entity is getting a laugh out of you. You’ve just painstakingly entered every stupid detail about yourself into a sign-up form, and then it strikes. Business as usual, right? You bite back a curse and diligently go through the entire ordeal once more.


But there it is again. It shouldn’t be, really. You’ve been careful this time, and to the best of your abilities, two and three do add up to five. Right? Right. Welcome to your own personal nightmare, you’ve found a captcha that doesn’t want to be solved.

There are a number of things that could cause it to behave this way. Worst case scenario, the captcha system hasn’t been implemented correctly. If you’re lucky, it’s one of your browser extensions acting up, interfering with the captcha’s normal routine; we can take care of that ourselves.

How Browser Extensions Can Interfere With Captcha’s

A lot of browser extensions or add-ons, like those that riddle your Chrome or Firefox install, use JavaScript to alter all, or some particular webpages after it’s been rendered. Some of those extensions, in particular, like to mess around with images on the page and don’t mix well with captcha’s.

captcha problems

Here’s one possible way this could go wrong. The page is loaded into your browser, along with a response field and a reference to your captcha image. Your extension gets a hold of the page, pulls up the images, and works its magic. However, the captcha it receives upon querying the server is generated anew, and the post-extension image no longer corresponds to the captcha response field. Oops.


Thankfully, it’s not the only way this story can turn out. Most image-manipulating extensions don’t mess up captcha’s, and a lot of more advanced captcha system are also immune to extensions of an inferior vintage. Even when the right combination of actors puts your captcha to ground, it’s an issue that’s easy to diagnose and to cure.

Is This What’s Happening To You?

The first thing to do is to open the page in another browser. Internet Explorer may be a necessary evil here. If it works, you’ve successfully isolated the issue to your other browser.

problems with captcha

Next, try to open the page in your regular browser, with your extensions or add-ons disabled. If you’re using Google Chrome, open an incognito window via File -> New Incognito Window. Firefox users should take a look at Saikat’s article on how to use Firefox safe mode How to Use Mozilla Firefox in Safe Mode Read More . If the problem has indeed disappeared, the fault was likely with one of your browser extensions.


Eliminate The Weak Link

To fix this problem once and for all, we have to find the weak link; the extension that’s been causing you all this trouble. Take a look at the list of extensions you have installed. Try to determine which of these plays around with images (some of them may have a broader use), and try the page again with these disabled. Iterate over the list, narrowing it down, until you’ve found the culprit extension(s).

captcha problems

What you do next is up to you. If it’s a sporadical issue, you may want to keep the extension enabled during regular Internet use. Once you’ve pinned down the troublemaker, it’s easy to toggle it off and on whenever you run into trouble. Alternatively, you can look for other extensions that deliver the same experience. A lot of simpler extensions are endlessly duplicated on the web, with differing implementations.

Have you ever run into issues with your add-ons or extensions?


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  1. Reý Aetar
    August 14, 2012 at 3:46 am

    horrible here the online passport appoinment site opens for only 1-2 mins for giving appointments but for some reason the captcha image is not loading in firefox or chrome so tried the captcha bypas addon (got to know about that from muo) but then the page stopped from loading but at last ie saved the day... slow but steady and never fails...atleast for me

  2. Bruce Epper
    June 19, 2012 at 2:32 am

    Any known culprits?

    • Simon Slangen
      June 19, 2012 at 6:37 am

      Two immediately come to mind. One, an extension that worked with animated PNG images. The other, an extension that enlarged thumbnails upon hovering over them.

  3. Paul-G
    June 18, 2012 at 11:56 pm

    Could that be the 'dreaded' addblock this site is always whitteing on about?

    • Bruce Epper
      June 19, 2012 at 2:31 am

      What is "whitteing"? Searched several online dictionaries and couldn't find it. Care to clue us in? Or at least me?

      • Prashant Mohta
        June 24, 2012 at 8:41 am

        he probably means white-listing....or he is using an alien lang. :)