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();
Promise { <state>: "pending" }