Join the AMA (Ask Me Anything) with the Firefox leadership team to celebrate Firefox 20th anniversary and discuss Firefox’s future on Mozilla Connect. Mark your calendar on Thursday, November 14, 18:00 - 20:00 UTC!

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

After Updating and loading message windw apears "TypeError: Components.classes[cid] is undefined" why and what to do?

more options

After upgrading to Firefox 6.0 after opening a small message window error opens with the message TypeError: Components.classes[cid] is undefined

After upgrading to Firefox 6.0 after opening a small message window error opens with the message TypeError: Components.classes[cid] is undefined

Asịsa ahọpụtara

This issue can be caused by an extension that isn't working properly.

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).

Gụọ azịza a na nghọta 👍 0

All Replies (2)

more options

Asịsa Ahọpụtara

This issue can be caused by an extension that isn't working properly.

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).

more options

Thanks cor-el I solved the problem The offender was "OneClick YouTube Downloader 1.07" I removed it and FireFox works OK