Firefox will popup an error in a number of situations. Most often this is caused by a misbehaving extension. = Disable common problem extensions = Before going through complicated troubleshooting steps, try disabling these extensions: #[[T:Open Add-ons|type=Extensions]] #If you see '''Orbit downloader''' or '''1-click YouTube downloader''' extensions, click the {button disable} button next to them. #*In the past McAfee SiteAdvisor, ZoneAlarm or PC Tools have also been problems. # Click {button Restart Firefox}. If the steps above didn't solve the problem, try these articles: *[[Troubleshooting extensions and themes]] *[[Add-ons are disabled after updating Firefox#w_check-for-new-versions-of-your-add-ons|Check for new versions of your add-ons]] *[[Software Update Failed]] *[[Error loading web sites]] *[[Uninstalling add-ons]] These related forum posts have answers by our top contributors. *[/questions/729606 Javascript pop errors stating: TypeError: Components.classes[cid] is undefined] *[/questions/714162 TypeError: EM.addUpdateListener is not a function I get this error eveytime I open FF] *[/questions/915232 Error: TypeError: xulItems[item].getAttribute] *[/questions/920074 Warning: nsIJSON.decode is deprecated. Please use JSON.parse instead] *[/questions/749513 TypeError: Components.classes <nowiki>['@mozilla.org/extensions/manager;1']</nowiki> is undefined]

Firefox will popup an error in a number of situations. Most often this is caused by a misbehaving extension.

Disable common problem extensions

Before going through complicated troubleshooting steps, try disabling these extensions:

1. Click the menu button , click Add-ons and themes and select Extensions.
2. If you see Orbit downloader or 1-click YouTube downloader extensions, click the disable button next to them.
   • In the past McAfee SiteAdvisor, ZoneAlarm or PC Tools have also been problems.
3. Click Restart Firefox.

If the steps above didn't solve the problem, try these articles:

• Troubleshoot extensions, themes and hardware acceleration issues to solve common Firefox problems
• Check for new versions of your add-ons
• How to fix the Update Failed error message when updating Firefox
• Websites don't load - troubleshoot and fix error messages
• Disable or remove Add-ons

These related forum posts have answers by our top contributors.

• Javascript pop errors stating: TypeError: Components.classes[cid is undefined]
• TypeError: EM.addUpdateListener is not a function I get this error eveytime I open FF
• Error: TypeError: xulItems[item.getAttribute]
• Warning: nsIJSON.decode is deprecated. Please use JSON.parse instead
• TypeError: Components.classes ['@mozilla.org/extensions/manager;1'] is undefined