There is a hotfix for this issue with disabled extensions released that is currently applied via a shield study and you only get this hotfix when studies are enabled.

See:

• https://support.mozilla.org/en-US/kb/add-ons-disabled-or-fail-to-install-firefox
• https://blog.mozilla.org/addons/2019/05/04/update-regarding-add-ons-in-firefox/

Did you not bother to actually read what I posted. I specifically stated that the hotfix has been applied and did not fix the problem.

Are both hotfixes applies or at least the one about intermediate certificate?

• hotfix-update-xpi-signing-intermediate-bug-1548973
• hotfix-reset-xpi-verification-timestamp-1548973

You could be experiencing this bug:

• Bug 1549078 - Some users indicating both Studies are active, but all extensions are still disabled

(please do not comment in bug reports
https://bugzilla.mozilla.org/page.cgi?id=etiquette.html)

Hi laserguy010, could you check whether the certificate was added. That would be on the Options/Preferences page:

• Windows: "3-bar" menu button (or Tools menu) > Options
• Mac: "3-bar" menu button (or Firefox menu) > Preferences
• Linux: "3-bar" menu button (or Edit menu) > Preferences
• Any system: type or paste about:preferences into the address bar and press Enter/Return to load it

In the search box at the top of the page, type cert and Firefox should filter to the Certificates section. Then click the "View Certificates" button. Check the "Authorities" tab to see whether Mozilla is listed with the new certificate. You can compare the attached screenshot.

If the certificate was NOT added:

Try one of the manual methods listed in this reply or the ones that follow it: https://support.mozilla.org/questions/1258208#answer-1218876

If the certificate WAS added:

Your Firefox should have triggered re-verification already, but you could try steps (2) and (3) in the above-referenced reply.

The certificate was not there but following your instructions, I downloaded and applied and now it's there and I can add new extensions. Thank you for that. It still will not let me reapply Kaspersky Protection as it shows it as a legacy extension and says it's no longer supported. Any idea how to get that extension back?

Extensions that aren't hosted on the Add-ons website may be using another certificate chain and may have to be signed again and updated by their developers.