Computer: Mac G5
Browser: Firefox 3.6.15
Unable to sign in with Firefox. In desperation tried Safari for this post, and it seems to be working fine so far. Trying to use Firefox, I wind up with the following "dead-end" message: "Captcha: Invalid code from image". Using Safari, I now have a positive indication that I have successfully signed in: the fourth word-group in the black line, above, now shows my screen name. Using Firefox, the third word-group always says "Sign In".
Hope this feedback is helpful, and that you will eventually get around to figuring out the Firefox issue. Thanks-