WebGL console warnings switching fullscreen

Steps to reproduce:

1. Build and Run a Unity project for Web
2. Press the Toggle Fullscreen button
3. Check the devtools console (F12)

Actual results: 
Performance warning: deleting framebuffer on context thread release!!!! WebGL: INVALID_OPERATION: drawBuffers: BACK or NONE

Expected results: 

Reproducible with versions: 

Not reproducible with versions: 

Can’t test with versions: 

Tested on (OS): 

Notes:

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