Extension signing is a requirement for all addons that will be installed on the release version of Firefox. This protects users from illegitimate addons that may damage the browser.

Please try downloading the most recent version of the Norton Safe tool bar. If that does not help, please contact Norton for further assistance.

The current issue with the Norton Identity Safe isn't due to 'signing' - which isn't disabling any add-ons, it just provides a warning message.

Please see Norton Support for answers regarding their add-ons for Firefox.