This site will have limited functionality while we undergo maintenance to improve your experience. If an article doesn't solve your issue and you want to ask a question, we have our support community waiting to help you at @FirefoxSupport on Twitter and/r/firefox on Reddit.

Search Support

Avoid support scams. We will never ask you to call or text a phone number or share personal information. Please report suspicious activity using the “Report Abuse” option.

Learn More

Error message at startup ug-in object: TypeError: Components.classes[cid] is undefined

more options

Mac 10.5.8 When I click alias for Firefox 4.ob-12 and now Firefox 4.0 I get the following error message that halts the startup until I click "Ok".

ug-in object: TypeError: Components.classes[cid] is undefined

What's wrong?

Mac 10.5.8 When I click alias for Firefox 4.ob-12 and now Firefox 4.0 I get the following error message that halts the startup until I click "Ok". ug-in object: TypeError: Components.classes[cid] is undefined What's wrong?

All Replies (5)

more options

Start Firefox in Diagnose Firefox issues using Troubleshoot Mode to check if one of the add-ons is causing the problem (switch to the DEFAULT theme: Tools > Add-ons > Themes).

  • Don't make any changes on the Safe mode start window.

See:

more options

It turned out that the McAfee Site Adviser extension was the problem. The last one I would have guessed. Thanks.

more options

Yep Site Advisor was the problem for me too.

more options

Alright, so here is the problem. The newest version of Firefox is Beta (Firefox 4.0). Unfortunately, SiteAdvisor does not work with this version, but they will be releasing an update, but I don't know when that will be.

Obviously, you want SiteAdvisor to work since it is warning you about potentially harmful sites, so here is the fix.

THE FIX: You must uninstall firefox and re-install version 3.6.16. Also, you may need to uninstall and re-install SiteAdvisor (this is necessary if site ratings are showing in Yahoo, but not other search engines like Google).

If you are using McAfee Internet Protection for Mac you may need to uninstall and re-install it as well. Again, this is necessary if site ratings are showing in Yahoo, but not other search engines like Google.

Hope this helps!!

more options

The MacAfee Site Advisor extension was the problem for me also. I have disabled it and the error message does not appear.