Extensions Last Updated date January 1, 2000
TorBrowser 7.0.5 (based on Mozilla Firefox 52.3.0) (64-bit) Linux (Ubuntu 16.04)
After extracting and loading a new TorBrowser instance, all extensions' Last Updated date is shown as January 1, 2000 (see screenshot).
about:addons -> Extensions -> More
This may be caused by the timestamps on the files in the xz, which are shown as 31 December 1999 19:00.