What site is it? So that I could see whether the website itself doesn't work. You can see captcha on this site (support.mozilla.com), I hope?

Update Java and Flash, please.

Start Firefox in Diagnose Firefox issues using Troubleshoot Mode to check if one of your add-ons is causing your problem (switch to the DEFAULT theme: Tools > Add-ons > Themes). See Troubleshoot extensions, themes and hardware acceleration issues to solve common Firefox problems and Troubleshoot issues with plugins like Flash or Java to fix common Firefox problems

See also Fix problems that cause images to not show

The captcha is not displayed when I want to login in gigapedia and also want to have a new account in yahoo messenger and others. why is that so?

The site says "This a browser setting issue. The images work properly, FireFox, IE and all other major browsers. "

http://www.servicetechhelp.com/h2desk/index.php?pid=knowledgebase#display_...

How do I set Firefox?

The captcha on this site is visible.

I do not think it is a browser problem. I went to the same sites with IE 8 and that browser did the same thing. No Captcha was viewable with that browser. thanx

I was experiencing this issue so went into Safe Mode as described above and went through testing my addons. Eventually I traced it to the Disconnect 1.0.1 extension which disables tracking software. Having disabled that addon I can now view Captcha on Firefox.