Then it's up to the Addon maker to update that they work with the latest browser version. So your going to have to contact the Addon maker to update their software.

^ignore the reply by markwarner22 as he is not aware of the why.

I have a very old version of Firefox (51.0.1 64-bit) on Windows 7 Pro. I know it's well out-of-date. Yesterday everything was fine. Today ALL the extensions have been disable because "[extension] could not be verified for use in firefox and has been disabled". There is no option to enable them again.

This is due to using the rather old version as you likely got a warning about the March 14 date in which extensions will be disabled. https://support.mozilla.org/en-US/kb/root-certificate-expiration

To not have your extensions disabled you need Firefox 128 or later or for Windows 7, 8, 8.1 and macOS 10.12, 10.13, 10.14 OS users you need Firefox 115.13.0esr at minimum though Fx 115.21.0esr is the current.

Is there any way to either enable the disabled extensions, or force firefox to reinstall then from my backups? I have toggled "xpinstall.signatures.required" to "false".

That preference only works in Extended Support Release and Developer Edition versions of Firefox. Your version 51 was just an ordinary release.

If you need to run extensions that are only compatible up to Firefox 56, and understand/accept that all these old versions are insecure/vulnerable and therefore not safe for general browsing on the wilds of the web, I think your best move is to transition your old installation to the Extended Support Release of Firefox 52. But make a backup of your profile first because it might not be possible to downgrade the data files after the update.

• See: Back up and restore information in Firefox profiles
• Download installer: https://archive.mozilla.org/pub/firefox/releases/52.9.0esr/win64/en-US/ -- if your prefer a local other than U.S. English, click the .. button on that page and then click into your preferred locale

Thank you James for the explanation as to why this has happened.

Thank you jscher2000 for a possible solution and the link. I'm crossing my fingers that it'll work for me.

Just to give you some insight into my mindset; I fix old clocks for living. I like keeping functional old things functioning :-)

Another solution is to change your Windows date back before March 13th since the 14th disabled extensions due to expired certs.

Another solution is to change your Windows date back before March 13th since the 14th disabled extensions due to expired certs.

Thanks for the suggestion, but sadly it does not work. All the extension remain disabled :-(

I'm guessing it's because firefox has flicked a switch in a file somewhere.

FYI

I just reinstated a 3-month-old backup of my firefox "profile" folder and turned back the clock on my PC. All my extensions came back to life :-)

So it would seem that there is a "switch" somewhere within the profile folder.

The old profile folder had date-time values recorded months ago. Here's why that matters:

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.

After changing the clock, you need to reset that value so Firefox doesn't wait. 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