Unless you run an unbranded builds ( https://wiki.mozilla.org/Add-ons/Extension_Signing#Unbranded_Builds https://wiki.mozilla.org/Add-ons/Extension_Signing#Unbr

Unless you run an unbranded builds ( https://wiki.mozilla.org/Add-ons/Extension_Signing#Unbranded_Builds https://wiki.mozilla.org/Add-ons/Extension_Signing#Unbranded... ), or the Developer Edition ( https://www.mozilla.org/en-US/firefox/developer/ https://www.mozilla.org/en-US/firefox/developer/ ), where setting xpinstall.signatures.required to false still works, then yes, Mozilla can prevent you from using an add-on. More than "going forward", this has been the case for a while now. It's been long enough ago that they disabled that setting in stock Firefox that I don't remember exactly when it happened.