Please test this in multiple browsers, with LTR and RTL language (Enabled RTL mode)  Login as Admin Setup and enable a Flickr public repository ( https://docs.moodle.org/38/en/Flickr_public_repository ). Create a Course. In the Course create a Forum activity. Go to the Forum. Click on "Add new discussion topic" button. Click on the "Insert or edit image" button in the "Message" rich text editor. Click on "Browse repositories..." button in the "Image properties" dialog. In the filepicker select the Flickr public repository In the "Full text" search field enter "Etruria, Stoke-on-Trent - park tree" (this is a name of an existing photo on Flickr with width > 3000px, you can use another photo as long as it's original width is larger than the screen width) Select to use the returned photo file. In the "Image properties" dialog make sure the dialog width does NOT extend beyond the screen width make sure the size of the image preview is the same as the photo's original size (or the one defined in the size inputs) but displayed within the size range of the dialog with scrollbars to preview the entire photo content.