According to [this question](http://stackapps.com/questions/3631/bug-in-the-stackexchange-api-getting-could-not-parse-proxy-url-when-user-not), the "could not parse proxy url" bug was solved more than 2 years ago.

However, when using the client-side OAuth flow, the aforementioned error message appears when executing `SE.authenticate`. Moreover, neither of `success` and `error` functions within `SE.authenticate` are executed. Instead, the user will be redirected to a page that tells him:

    Application Login Failure
    
    An error occurred while login into an application.
    Error Details
    
    error description: could not parse proxy url

although the login **is** successful, as the username appears in the page top navbar.

I encountered this error while developing a Firefox add-on that uses Stack Exchange API. You can confirm the bug by visiting [this SE documentation page](https://api.stackexchange.com/docs/js-lib) and clicking on the **demo "Run Example" button** at the bottom of the page.