It should be the same for STEAM and non-STEAM versions, as far as I found in the net.
Start the game once:
Start the game at least once and configure your settings etc. After this the directory and some files (like "UserSettings.txt") should be created.
After that:
Assuming your windows username is "
momothebear" and your are playing on the US servers, the folder should be:
Code:
C:\Users\momothebear\Documents\Elder Scrolls Online\live\AddOns\
If you are playing on the EU servers the path would be:
Code:
C:\Users\momothebear\Documents\Elder Scrolls Online\liveeu\AddOns\
If the "AddOns" directory is missing just create it manually (watch the capital "O").
Manually download the addons from here and unzip the archives into the "AddOns" folder.
Or use the "Minion" addon manager to automatically do it for you, and update the addons.