Deleting Cert8.db for Firefox

Make sure you've tried other alternatives before deleting cert8.db. Often, not being able to delete certificates in Firefox is caused by a bug with the master password. For a less invasive workaround, see this article.

On this page:

Context

People in the MIT community attempting to clear expired certificates from Mozilla Firefox.

Cause

Firefox stores certificates separately from the Operating System. Sometimes the certificate store can become corrupt and won't let you delete certificates. To solve this, you'll have to reset it manually.

Solution

This will delete all your Firefox personal certificates, as well as the MIT Certificate Authority. Be sure to export any certificates you wish to keep.

Windows

1. Press Winkey+R to open up the Run window (the Windows key is located between alt and ctrl). The following window should appear:
   
   
2. Type %appdata% and click Ok.
   Result: A folder should open up.
   
   
3. Now go to Mozilla, then Firefox, then Profiles, and choose your profile folder (it probably is named a random string of letters, often followed by .default).
   
   
4. Delete the file called "cert8.db".
5. Install new certificates by going to https://ca.mit.edu/ca/ in Firefox and following the instructions there.

Mac OS X

1. While in the Finder, click the Go menu, then click Go to Folder. The following window should open:
   
2. The folder will be in one of two locations:
   ~/Library/Mozilla/Firefox/Profiles/
   ~/Library/Application Support/Firefox/Profiles/
3. Once you've found your profile folder, go into it and delete "cert8.db".
   
4. Install new certificates by going to https://ca.mit.edu/ca/ in Firefox and following the instructions there.

Linux

1. The profile folder is located in ~/.mozilla/firefox/. You can get there by using the cd command in terminal or by navigating there in your file viewer. Note that .mozilla is a hidden folder.
2. Once you're in your profile folder, delete "cert8.db". This can be done through your file viewer or with the rm command in terminal.
3. Install new certificates by going to https://ca.mit.edu/ca/ in Firefox and following the instructions there.