Yes, provided that you installed it either from addons.mozilla.org or eff.org. * https://en.wikipedia.org/wiki/Electronic_Frontier_Foundation The vast majority of add-ons aren't digitally signed, which is why the installation prompt shows "(Author not verified)". This holds true even for [https://addons.mozilla.org/firefox/user/mozilla/ add-ons made by Mozilla]. The only signed add-ons I can think of are Adblock Plus and Element Hiding Helper for Adblock Plus. From [https://addons.mozilla.org/faq the frequently asked questions page]: <blockquote>'''Are add-ons safe to install?'''<br> Unless clearly marked otherwise, add-ons available from this gallery have been checked and approved by Mozilla's team of editors and are safe to install. We recommend that you only install approved add-ons. If you wish to install unapproved add-ons or add-ons from third-party websites, use caution as these add-ons may harm your computer or violate your privacy. [https://addons.mozilla.org/developers/docs/policies/reviews Learn more about our approval process]</blockquote>

Thank you very much for the detailed answer.