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Fix: Firefox 35 can’t install add-ons and extensions

Firefox just updated itself to version 35 on my current PC. I tried to install a new add-on (Session Manager, in case you are curious) but it failed to install for no reason. It gave the error message Add-on could not be installed because Firefox cannot modify the needed file.
Add-on could not be installed Firefox 35
Here is how you can resolve this issue if it ever happens on your PC.

The problem is in the new default settings in Firefox 35. Due to some bug, Firefox 35 was released with the client-side storage API disabled! This causes various other issues besides the one mentioned in this post: my previous browsing session also could not be restored. Popular add-ons like AdBlock or Ghostery eventually stop working too.
Here is how you can fix the issue:

  1. Open a new tab and enter the following text in the address bar:
    about:config

    Confirm that you will be careful if a warning message appears for you.

  2. Enter the following text in the filter box:
    dom.indexedDB.enabled

    dom.indexeddb.enabled

  3. You will see the parameter dom.indexedDB.enabled. It is set to false which is wrong. Set it to true:
    dom.indexeddb.enabled true

This will resolve all issues caused by the wrong Firefox configuration. No browser restart is required. In my case, I could install the add-on immediately:
fixed
That's it. Hopefully this will be helpful to you.

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Author: Sergey Tkachenko

Sergey Tkachenko is a software developer who started Winaero back in 2011. On this blog, Sergey is writing about everything connected to Microsoft, Windows and popular software. Follow him on Telegram, Twitter, and YouTube.

5 thoughts on “Fix: Firefox 35 can’t install add-ons and extensions”

  1. Are you sure it’s Firefox “default” setting? I had NO problems at all after v35 update. And I’ve “dom.indexedDB.enabled” set to “true”. It was not false.

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