This is due to https://support.mozilla.org/en-US/kb/root-certificate-expiration

To not have Extensions be disabled and to be able to install new Extensions one needs Firefox 128 or later or Firefox 115.13.0esr or later (currently at 115.21.0esr).

The last version to still support the old eol macOS 10.9, 10.110, 10.11 was the old Firefox 78.15.0esr which has not been updated since October 5, 2021.

However if your hardware does allow for your macOS to be updated to 10.12 or later then you would be able to use Firefox 115 ESR. https://support.mozilla.org/en-US/kb/firefox-users-macos-1012-1013-1014-moving-to-extended-support

Cant update to 115.13.0esr. I'm not really code savvy but find it hard to believe there is no way to protect older os users ( 78.15.0esr users) with basic privacy extensions- All privacy add-ons seen as "corrupt"- Was reading about way to use thru advanced settings but must be knowledable in this regard. Loved mozilla and its whole way of operating and philosophy of use for many years but seems like things have changed... Maybe just me ( not changing os)

Thanks for your time and the info

The Extended Support Release of Firefox 78 can be set not to require a valid extension signature. This obviously is risky because then Firefox will happily run extensions never reviewed/cleared/signed by Mozilla. But it is an option if your extensions are critical and you accept that risk. See the last section of the following article:

Add-on signing in Firefox

There is a date-time value in the prefs.js file (editable through about:config) which determines the time when Firefox next tries to re-verify your extensions. You may need to reset that value so Firefox doesn't wait until tomorrow. Here's how:

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

More info on about:config: Configuration Editor for Firefox. The moderators would like us to remind you that changes made through this back door aren't fully supported and aren't guaranteed to continue working in the future.

(2) In the search box in the page, type or paste xpi-signature-verification and pause while the list is filtered

(3) Click the trash can at the right end of the row for the app.update.lastUpdateTime.xpi-signature-verification preference to remove this preference

(3) Do a normal exit/restart of Firefox, and within about a minute Firefox should reverify your extensions