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Error details: all images can not be opened after clicking on preview. Firefox from "Firefox Beta" PPA. KUbuntu 16.04
error: could not load image from https://upload.wikimedia.org/wikipedia/en/d/db/Exon_and_Intron_classes.png
user agent: Mozilla/5.0 (X11; Linux x86_64; rv:57.0) Gecko/20100101 Firefox/57.0
screen size: 1920x1080
canvas size: 1900x831
image size: 394x345
thumbnail size: CSS: 947x831, screen width: 947, real width: 1024