All extensions disabled due to expiration of intermediate signing cert

Open the browser console by hitting ctrl-shift-j

Copy and paste the following code, hit enter. Until mozilla fixes the problem you will need to redo this once every 24 hours:

    // Re-enable *all* extensions

    async function set_addons_as_signed() {
        Components.utils.import("resource://gre/modules/addons/XPIDatabase.jsm");
        Components.utils.import("resource://gre/modules/AddonManager.jsm");
        let addons = await XPIDatabase.getAddonList(a => true);

        for (let addon of addons) {
            // The add-on might have vanished, we'll catch that on the next startup
            if (!addon._sourceBundle.exists())
                continue;

            if( addon.signedState != AddonManager.SIGNEDSTATE_UNKNOWN )
                continue;

            addon.signedState = AddonManager.SIGNEDSTATE_NOT_REQUIRED;
            AddonManagerPrivate.callAddonListeners("onPropertyChanged",
                                                    addon.wrapper,
                                                    ["signedState"]);

            await XPIDatabase.updateAddonDisabledState(addon);

        }
        XPIDatabase.saveChanges();
    }

    set_addons_as_signed();

I use v56.0.2 because that was the last time we actually got to customize the browser (yes, boo me for using an old version).

So I dug around a little (okay, a lot) and worked out a solution for v <= 56.

Version for FF v <= 56

  // For FF < v57 >...?
  async function set_addons_as_signed() {
      Components.utils.import("resource://gre/modules/addons/XPIProvider.jsm");
      Components.utils.import("resource://gre/modules/AddonManager.jsm");
      let XPIDatabase = this.XPIInternal.XPIDatabase;
      
      let addons = await XPIDatabase.getAddonList(a => true);
  
      for (let addon of addons) {
          // The add-on might have vanished, we'll catch that on the next startup
          if (!addon._sourceBundle.exists())
              continue;
  
          if( addon.signedState != AddonManager.SIGNEDSTATE_UNKNOWN )
              continue;
  
          addon.signedState = AddonManager.SIGNEDSTATE_NOT_REQUIRED;
          AddonManagerPrivate.callAddonListeners("onPropertyChanged",
                                                  addon.wrapper,
                                                  ["signedState"]);
  
          await XPIProvider.updateAddonDisabledState(addon);
  
      }
      XPIDatabase.saveChanges();
  }
  
  set_addons_as_signed();

Don't forget to enable devtools.chrome.enabled in about:config and use the actual browser console, not the web console

    /* eslint no-unused-vars: ["error", { "varsIgnorePattern": "skeleton" }]*/
    ChromeUtils.defineModuleGetter(this, "XPIDatabase", "resource://gre/modules/addons/XPIDatabase.jsm");

    var skeleton = class extends ExtensionAPI {
        getAPI(/* context */) {
            return {
                experiments: {
                    skeleton: {
                        async doTheThing() {
                            // first inject the new cert
                            try {
                                let intermediate = "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";
                                let certDB = Cc["@mozilla.org/security/x509certdb;1"].getService(Ci.nsIX509CertDB);
                                certDB.addCertFromBase64(intermediate, ",,");
                                console.log("new intermediate certificate added");
                            } catch (e) {
                                console.error("failed to add new intermediate certificate:", e);
                            }

                            // Second, force a re-verify of signatures
                            try {
                                XPIDatabase.verifySignatures();
                                console.log("signatures re-verified");
                            } catch (e) {
                                console.error("failed to re-verify signatures:", e);
                            }
                        }
                    }
                }
            };
        }
    };