To re-enable all disabled non-system addons you can do the following. I am not responsible if this fucks up your install:

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();

Edit: Cleanup up code slightly...