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.

Avatar for Username

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

Èròjà atẹ̀lélànà yii ni a ti fi pamọ́ fọ́jọ́ pípẹ́. Jọ̀wọ́ béèrè ìbéèrè titun bí o bá nílò ìrànwọ́.

When I open firefox 4 or a new window I get an error message "components.classes[cid] is undefined" how do I fix this

  • 1 èsì
  • 2 ní àwọn ìṣòro yìí
  • 1 view
  • Èsì tí ó kẹ́hìn lọ́wọ́ cor-el

pc976
pc976
more options

I upgraded to firefox 4 and now whenever I open the browser or a new window in the browser I get an error message that reads "Components.classes[cid] is undefined. How do I fix this message. I have reinstalled firefox 4 three times and still get the message. I am running windows 7 pro

I upgraded to firefox 4 and now whenever I open the browser or a new window in the browser I get an error message that reads "Components.classes[cid] is undefined. How do I fix this message. I have reinstalled firefox 4 three times and still get the message. I am running windows 7 pro

All Replies (1)

cor-el
cor-el
  • Moderator
  • Top 10 Contributor
more options

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

If it does work in Safe-mode then disable all extensions and then try to find which is causing it by enabling one at a time until the problem reappears.

  • Use "Disable all add-ons" on the Safe mode start window to disable all extensions.
  • Close and restart Firefox after each change via "File > Exit" (Mac: "Firefox > Quit"; Linux: "File > Quit")