The 3D Warehouse has not supported MSIE for at least a year (since MAR 2018.)
The Extension Warehouse has just been overhauled to run on the same framework / backend (whatever it’s called) as the 3D Warehouse. This is why they have the same Technical Problems category (where I’ve moved this thread.)
Here is an official announcement here in the forum:
Also colin just posted a notice that Discourse (who host this forum) will cease supporting MSIE next June.