Firefox not letting members join

[shamus mcquail]

So I had a member that was trying to join with firefox.  It kept telling him the security code answer was wrong.  He went to the edge browser and it worked first time.  Is this common?

[GregChapman]

I thought I recalled similar issues being reported a while back. Perhaps it never was fixed. See:
http://support.nabble.com/Captcha-error-td7503021.html