I downloaded several add-ons. I have discovered that do not like them, and want to delete them. However, I cannot find a way to do that. The add-ons that want to delete are Feedly, Similar Web, and Xmarks.
Windows Vista Home Editon Premium
See Disable or remove Add-ons
You can uninstall ad-ons in the Add-ons Manager: Tools > Add-ons > Extensions