How-To Geek

Work-Arounds for Failed Extension & Theme Installs in Firefox

Have you ever tried to install an extension or theme in Firefox and received the irritating “Invalid file hash (possible download corruption)” error message? Now you can work on resolving that problem with the following work-arounds.

The Infamous Message Window

This is probably the most irritating message window that is associated with installing extensions or themes in Firefox. For whatever reason, you start the installation and get this. Not good at all! So what do you do about it?


Possible Work-Arounds

Try the following methods to see if one will help get those problem extensions or themes installed.

Method 1 – Enable Third Party Cookies

  1. Go to the Tools Menu and select Options.
  2. Once the Options Window is open, choose the Privacy Tab
  3. Select “Use custom settings for history” to in order to access the additional options
  4. Make certain that “Accept third-party cookies” is selected
  5. Click “OK”. (Restarting Firefox is recommended)


Method 2 – Manually Install The Extension

  1. Right click on the extension or theme install link and select “Save Link As”
  2. Once you have saved the extension or theme, drag the file into the Add-ons Manager Window with your mouse

Note: If for some reason manually installing the extension or theme still fails, there is a possibility that your anti-virus or another download monitoring software may be corrupting the file. In this case you could download the extension or theme on another computer and transfer it using a flash drive.

Method 3 – Clear The Cache

  1. Go to the Tools Menu and select Options.
  2. Once the Options Window is open, choose the Privacy Tab
  3. Select “Use custom settings for history” to in order to access the additional options
  4. Select “Clear history when Firefox closes” and then click on the “Settings Button”
  5. Make certain that “Cache” is selected in the Settings Window (other options can all be deselected based on your needs)
  6. Restart Firefox

invalid-03 invalid-04

Method 4 – Restart Firefox After “Failed Add-on Installation”

  • If you are installing directly from the Mozilla Add-ons website, there could be a problem with the Mozilla Add-ons website database or with a broken mirror website. Restart Firefox to see if the extension or theme did install regardless of the“Invalid file hash (possible download corruption)” error message.

Method 5 – Other Alternatives

  1. Try installing the extension or theme again at a later time
  2. Try installing the extension or theme from the add-on creator’s personal website

Hopefully with these tips you can bypass the error and enjoy more Firefox Add-on goodness.

Akemi Iwaya is a devoted Mozilla Firefox user who enjoys working with multiple browsers and occasionally dabbling with Linux. She also loves reading fantasy and sci-fi stories as well as playing "old school" role-playing games. You can visit her on Twitter and .

  • Published 08/4/09

Comments (4)

  1. RottNKorpse

    Nice article but just wanted to add there is another possible reason. If you are trying to install an “experimental” extension, an extension still in the Firefox Sandbox, there is a checkbox to mark to allow you to download said extension but sometimes that will result in the error. To fix that and let you install the experimental addon all you need to do is sign up for an account at the firefox addon site and login.

    That doesn’t happen very often but I have encountered that error a couple times when not logged in.

  2. Santo

    The latest version of Firefox 3.5.1 does not have the same options as given in the above screen shots.

  3. AnotherWay

    There is another way. It’s the only way to install plugins that are not being updated.

    Find the extension you want to install. Right click on the “Add To Firefox” button and save the extensions install file (usually a .jar or .xpi file). Now use WinRAR to extract the files to a folder. You should see a few files/folders now.

    Open the file named “install.rdf” with notepad.
    Towards the bottom you should see this line:

    Change the number to 3.5.*
    Save the change and repack it. Now drag the repacked file into the FF AddOns window and you’re good to go.

    This has worked every time for me.

  4. AnotherWay

    Sorry. Forgot that the line would be read wrong.

    The line you’re looking for is:
    em:maxVersion >3.5.*< /em:maxVersion

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