Hi, I can't find this extension on AMO. Is it self-distributed? You have to re-sign it, because our certificates has been changed.

For developers of add-on versions self-distributed that were uploaded prior to April 5, 2019.

• Action will be required as Mozilla is not able to automatically re-sign unlisted versions since the distribution is controlled by the developer and thus the AMO team cannot determine which version(s) to re-sign
• Action required: To continue to distribute any self-hosted versions uploaded to AMO prior to Apr 5, 2019, developers will need to submit new versions to AMO.

Self-distributed add-on versions that are not re-submitted by Apr 15 will no longer be installable on any version of Firefox 127: Nightly (Apr 15), Beta (May 13) or Release (Jun 11). Add-ons installed prior to Firefox 127 will continue to work for now, but we ask that you encourage your users to upgrade to the new, re-signed version of your add-on once you have re-submitted it to AMO. Any previous versions that are no longer in use do not need to be re-submitted to AMO.

Our company's firefox add-on(Saba Security Plugin) has stopped working, please let me know what happened. I have already contacted you once at: product-help@firefox.com

Perhaps you could ask about your Extension issues at https://discourse.mozilla.org/c/add-ons/35

Where did you find that email? as Mozilla does not provide one on one support by phone, chat or email, especially not for a free to download and use application. Mozilla does have a direct ticket system for their subscription based products though.