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error message before Firefox will start up, "what happened:TypeError: Components.classes['@mozilla.org/extensions/manager;1'] is undefined"


When ever I try to start up Firefox I get this message which I have to accept before Firefox will start.

"what happened:TypeError: Components.classes['@mozilla.org/extensions/manager;1'] is undefined"

This only started since I installed version 4.03 and has continues to date.

Chosen solution

Same for me--uninstalling it made the problem go away.

Read this answer in context 6

Additional System Details

This happened

Every time Firefox opened

This started when...

upgraded to Firefox version 4.03

Installed Plug-ins

  • Shockwave Flash 10.1 r82
  • Next Generation Java Plug-in 1.6.0_21 for Mozilla browsers
  • NPRuntime Script Plug-in Library for Java(TM) Deploy
  • 4.0.50524.0
  • Office Live Update v1.5
  • Adobe PDF Plug-In For Firefox and Netscape "9.3.3"
  • The QuickTime Plugin allows you to view a wide variety of multimedia content in Web pages. For more information, visit the QuickTime Web site.


  • User Agent: Mozilla/5.0 (Windows NT 6.1; rv:2.0b4) Gecko/20100818 AskTbBT5/ Firefox/4.0b4

More Information

  • Top 10 Contributor
  • Moderator
10761 solutions 96861 answers

Start Firefox in Troubleshoot Firefox issues using Safe 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

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

You can use "Disable all add-ons" on the Troubleshoot Firefox issues using Safe Mode start window to disable all extensions.

You have to close and restart Firefox after each change via "File > Exit" (Mac: "Firefox > Quit"; Linux: "File > Quit")

You may also need to delete extensions.sqlite in the Firefox Profile Folder

nebdan 0 solutions 1 answers

Helpful Reply

I noticed that Foxit reader installed the ASK tool bar (even though I chose not to have it installed) after uninstalling it from the Addons area the error stopped.

roymustang 0 solutions 1 answers

Helpful Reply

It was Ask tool bar for me too

cvhyphus 1 solutions 1 answers

Chosen Solution

Same for me--uninstalling it made the problem go away.

Question owner

Many thanks to one and all it was the Ask and Yahoo toolbars that seem to have caused it, even though, like many others I had said I don't want it, it was installed. So thanks all problem now solved. Keith