Use the USPS postage calculator w/o its Javascript v1.1resigned1
Allows you to use the USPS postage price calculator at postcalc.USPS.com on IceCat without disabling LibreJS or running the website's Non-free Javascript.
This add-on assumes that you are running LibreJS and was tested on the latest version of GNU IceCat, a version of Firefox.
For more info about non-free Javascript and why it should be avoided:
https://www.gnu.org/philosophy/javascript-trap.en.html