Firefox does not display Captcha box
Firefox 33.1 does not display captcha boxes. this is not new has been ongoing for a year or more and I keep a copy of IE installed so that when I find a site that tells me I have not entered the captcha correctly (The one that I didn't see at all) i can go into IE and work in there.
ప్రత్యుత్తరాలన్నీ (2)
Many CAPTCHAs on the web are hosted by Google (reCAPTCHA). It's possible that one of your extensions is blocking this and needs to have an exception added. I would check particularly whether Google Disconnect could be involved.
Actually, you might not have noticed this, but Disconnect is no longer updating the separate Google Disconnect and Facebook Disconnect extensions, and has created a consolidated extension that replaces those and has new features.