icecat source package contains files "with a time stamp too far in the past"

The Icecat source package contains many files, in extensions/gnu, with a timestamp older than 1980-01-01. These files are rejected by buildsystems such as Launchpad. I have had 8 builds fail because of this: https://launchpad.net/~legimet/+archive/ubuntu/abrowser-kde/+builds?build_text=&build_state=uploadfail, so these files should have their timestamps updated.