Media Browser in WYSIWYG editor doesn't allow uploads for non-admins
There are two things need to be configured for WYSIWYG editor. 

First settings can be found on admin/config/media/browser. Either you check all available plugins like you have done in screenshot or leave all unchecked for allowing all. That's already done by you.

Next is to check permissions, where you have to give Add and upload new files, view own files etc permissions (like my screenshot below)



Another permission to check is Use media browser, which you must have done &amp; so that it's appearing. Once these are in place, it should work for the role you are checking.