Firefox Adds-on Manager cannot verify add ons

The Adds-on Manager of my Firefox browser issued two messages:
Zotero could not be verified for use in Firefox and has been disabled. Zotero (disabled).
Zotero LibreOffice integration could not be verified for use in Firefox and has been disabled. Zotero LibreOffice Integration 3.5.9 (disabled).
On Jul 18, 2017 I installed Zotero 5.0.4 successfully. The installation of the add-in to integrate Zotero with LibreOffice was also successful. I was using the Safari browser instead of Firefox during both installations.
Firefox 54.0.1
macOSSierra 10.12.5
Zotero 5.0.4
  • Zotero 5.0 is only a standalone application, not an extension for Firefox. What you currently have installed in Firefox are very very old versions of Zotero. You should install the newly released Firefox connector plugin from, which will connect with the standalone Zotero application.
  • Thank you, bwiernik.
    This message appeared after I downloaded the Zotero Connector for Firefox:
    The add-on downloaded from could not be installed because it appears to be corrupted.
    What's the solution?
  • edited July 19, 2017
    Can you tell us the site certificate info you see for both and

    The fact that you're getting this message, and that you weren't getting Firefox extension updates, suggests something on your computer or network may be intercepting your connections.
  • The site certificate info for both and is the same; i.e.,
    Verified by Avast.
    This certificate has been verified for the following uses: SSL Server Certificate.
    Issued to:
    Common Name (CN) *
    Organization (O)
    Organizational Unit (OU)
    Serial Number 05:27
    Issued by:
    Common Name (CN) Avast Trusted CA.
    Organization (O) Avast
    Organizational Unit (OU) Software development
    Period of Validity:
    begins on Oct 29, 2016
    expires on Nov 3, 2-18.
  • OK, right, so Avast's HTTPS-scanning feature is breaking things for you. See Updates Not Detected for more details, with one difference:
    Normally Firefox prevents manual installations over such connections as well, but we have implemented a workaround to allow them.
    This part isn't currently implemented after a recent update to the downloads page, so you'll need to either temporarily (or permanently) disable the HTTPS interception in Avast or download the connector XPI to disk (right-click -> Save Link As…) and then drag it into Firefox.
  • Hi dstillman,
    I disabled the HTTPS interception in Avast.
    The download and installation of the Zotero Connector to Firefox was successful.
    Big Thanks!!
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