In the plex web portal under account, when you click “choose photo” then hit cancel on the file browser that appears, the file browser re opens again in an infinite loop. I had to force close the running browser process to get the file browser window to go away.
This error appears in Microsoft Edge Browser, latest stable version 38.14393.0.0, no addons/extensions installed, in windows 10 on localhost.
I have tested it in chrome (latest stable) and the file browser closes properly.
Just wanted to submit this little bug I found. 
_ EDIT _
Forgot to mention the plex server is running version 1.3.3.3148