The 1841 British edition accidentally replaced our with your, probably because of the use of your in the immediately preceding parallel question in this verse: “have ye forgat the commandments of the Lord your God”. The original our was restored to the LDS text in the second printing of the 1852 edition, probably as a result of consulting the 1840 edition.
Summary: Maintain in Alma 60:20 the original our in “have ye forgat the captivity of our fathers”.