This tutorial compliments the existing documentation about setting up media source's permissions for the default Content Editor access policy:
Originally, content editor can not access the files in Media Browser to select or upload new file/images. If you need it as such, like having image based Template Variable, you need to change the default permission of the Content Editor usergroup.
Select Access Control List from right side menu.
Right click on the "Content Editor" row and select "Update Policy"
Then you need to change some permissions that the toolbar requires to show button to list file, upload file, and/or create directory.
On your browser, just search these settings and make them enabled/checked:
If you want the Content Editor usergroup has Files tree on the left navigation, enable this setting as well:
If you want to show some context menu (right-click menu) on the Files tree, you need to enable any of these settings as well:
You can read through that
getListContextMenu() function and select which other permissions you need them enabled, by searching this text
I hope this can answer the riddles of adding permission for Content Editor to make them able to access the file system in MODX Revolution.