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In Firefox Mozilla, repeating pop-up says Type Error:components.classes (cid) is undefined. I think it`s something to do with Javascript.

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In a drop-down box (pop-up) I repeated get the above message under the bracketed heading of JAVASCRIPT APPLICATION, andI cant permanently delete it.

In a drop-down box (pop-up) I repeated get the above message under the bracketed heading of JAVASCRIPT APPLICATION, andI cant permanently delete it.

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Tools > Error Console - look for that message in the Error Console - right-click it and use Copy, then paste that message into the Reply box here. There should be something in that error message that will help us identify the source of that fault.

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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")

In Firefox 4 you can use one of these to start in Safe mode:

  • Help > Restart with Add-ons Disabled
  • Hold down the Shift key while double clicking the Firefox desktop shortcut (Windows)