The Captcha images fails with some Firefox add-ons, like Firebug. It appears that Firebug first loads the image and then the browser loads another different image. Entering the text for the Captcha in Firebug passes verification but the one shown on the browser fails.

This has become a problem with some users with other Firefox add-ons (not exactly sure what ones yet). Is anyone aware of a work-around other than disabling add-ons?