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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

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?

All Replies (1)

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)