As you may know, Bitdefender intercepts your browsing to filter the websites' responses and in order to decrypt and read the secure ones, it needs to present fake certificates to Firefox.

Did your Firefox perform a Refresh during your update? Or were you using version 43 before you reinstalled Windows? In other words, I guess, do you have a copy of your old profile folder? In the case of a Firefox Refresh, it should be on the desktop inside an Old Firefox Data folder. Otherwise, it might only be in a backup you created.

If you do not have a copy of your old profile folder, you could check with Bitdefender on the official solution to the problem.

Here are two other possible workarounds:

Import the Bitdefender Certificate that Signs the Fake Site Certs As A Trusted Authority

The general process for this is:

• Export the certificate from the Windows Certificate Store (e.g., through Internet Explorer's certificate viewer)
• Import the certificate into Firefox's Certificate Manager

An example is in this thread: https://support.mozilla.org/questions/1068675#answer-745280

Let Firefox Trust Anything Windows Trusts

This is a recently added setting and the full security implications are not yet clear; it does seem to make you more vulnerable than the previous method. You can try it as follows:

(1) In a new tab, type or paste about:config in the address bar and press Enter/Return. Click the button promising to be careful.

(2) In the search box above the list, type or paste roots and pause while the list is filtered

(3) Double-click the security.enterprise_roots.enabled;false preference to switch the value from false to true

Update on bitdefender issue . If you update Bitdefender does the problem go away ?

Bitdefender FREE AV version was recently causing crashes and hangs in Firefox 53. Sometime yesterday the Bitdefender people rolled back their problem update of Bitdefender. If you make sure your Bitdefender is fully up to date then as far as we know at present that should not have bad effects on Firefox.

Forum Note:

• See: Contributors thread: https://support.mozilla.org/en-US/forums/contributors/712411#post-71647
• Note bug1363332#c14

  We've issued a rollback while we investigate (note, this only affects AVfree users). Please try an update and see if the issue still occura.
  Thanks!

  • https://bugzilla.mozilla.org/page.cgi?id=etiquette.html