In the "Add-ons Manager" I have extensions that say things like "Extension X (disabled)". I simply want to get rid of them. Yet, I can find no way to delete or remove any add-ons, extensions or plug-ins using the "Add-ons Manager". Can someone explain to me: (A) Is there a difference between an add-on, an extension, and/or a plug-in? (B) How do I remove the ones that appear in the extensions list, if I want to? (C) How could anyone write software that allows you to add something without also allowing you to delete it (or hiding that function so thoroughly that neither the support help nor Google will disclose it)? Thank you.