This is not due to an update, but just the passage of time. Older versions of Firefox have NOT been updated with the latest certificate needed to verify extensions, which is why they get disabled. For background, see:

Update Firefox to prevent add-ons issues from root certificate expiration

Can you update Mac OS on your system? If you can run Sierra, you can get on the current Firefox 115 Extended Support Release series. I've read that visiting the Mac App Store in Safari is the best way to determine compatibility with Mac OS upgrades.

If not, you can set Firefox not to verify extensions. This does increase the risk that malware will slip in, but presumably you are extremely careful with what you install because you already run an old OS. For more information on this option, see the last section of the following article: Add-on signing in Firefox.

All my addons have disappeared after a firefox update. 78.15 Oesr,

The old Firefox 78 ESR has not been updated since 78.15.0esr released back on October 5, 2021.

Firefox 79.0 to 115 ESR requires macOS 10.12, 10.13, 10.14 to run while Firefox 116.0 to current requires macOS 10.15 or later to run.

If your hardware allows you to update your macOS from 10.11 to 10.12 or later then you can run Firefox 115 ESR.