Seems that image at https://commons.wikimedia.org/wiki/File:Toolbaricon_definition_list.png got corrupted. It is being used in some gadgets. I don't see any edits in past years, so I'm not sure, what could have brake it.
Details of the error are attached to the report, which will be publicly viewable. If you are not comfortable with that, you can edit the report below and remove all the data you don't want to share.
error: could not load image from https://upload.wikimedia.org/wikipedia/commons/a/a8/Toolbaricon_definition_list.png
user agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:50.0) Gecko/20100101 Firefox/50.0
screen size: 1536x864
canvas size: 1519x679
image size: 22x22
thumbnail size: CSS: 679x679, screen width: 848.75, real width: 1024