This does appear to be a privacy feature in IceCat. To report the correct timezone offset, go to about:config" and disable "privacy.resistFingerprinting" then restart IceCat.
Note that toggling "privacy.resistFingerprinting" immediately changed the result of `new ate().toString()` on all tabs, but `new Date().getTimezoneOffset()` was changed only on the about:config tab. After a restart all tabs showed the correct offset. See this IceCat bug report discussion: https://lists.gnu.org/archive/html/bug-gnuzilla/2019-06/msg00010.html Regards, Ben
