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When attempting to install add-ons, Firefox generates a message saying it is unable to install add-on because Firefox cannot modify the necessary file. To what file is this referring, and how do I fix this problem?

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  • Last reply by cor-el

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When I download an add-on such as Colorful Tabs and start the installation process, I receive a message that Firefox cannot install the add-on because it cannot modify the necessary file. To what file is this referring?

When I download an add-on such as Colorful Tabs and start the installation process, I receive a message that Firefox cannot install the add-on because it cannot modify the necessary file. To what file is this referring?

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That is usually caused by Firefox not unpacking the extension.

You can try to set the Boolean pref extensions.alwaysUnpack to true on the about:config page.

To open the about:config page, type about:config in the location (address) bar and press the "Enter" key, just like you type the url of a website to open a website.
If you see a warning then you can confirm that you want to access that page.

  • Use the Filter bar at to top of the about:config page to locate a preference more easily.
  • Preferences that have been modified show as bold (user set).
  • Preferences can be reset to the default via the right-click context menu if they are user set
  • Preferences can be changed via the right-click context menu: Modify (String or Integer) or Toggle (Boolean)