In T115563#4945918, @Tgr wrote:

@Jwpat7 you need to refresh the page, then enter the code before opening any images in MediaViewer, then try opening an image. Apart from that what you do with the console doesn't matter (although if you leave it open there's a chance it gives you some useful error message when opening the image fails).

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Regarding the problem with an error screen appearing after clicking a small image (with message "Sorry, the file cannot be displayed" "There seems to be a technical issue"): This message occurs when I click on images on the page https://en.wikipedia.org/wiki/Dilution_refrigerator using browser "Chromium Version 71.0.3578.98 (Official Build) Built on Ubuntu , running on Ubuntu 18.04 (64-bit)".