When I click on an image in a post that is above 1200px, it opens as a new window. When I then click on the little green button in the left corner it enlarges to a full-screen size, as it should. But... it does so in a new "space" as Apple calls it, i.e., a separate desktop. Once there, it is impossible to close it without killing the browser (Chrome) first. The little red, orange, green radio buttons are missing from the window, and "escape" key does nothing. Apple Yosemite has a separate way of "killing" a space (by positioning the cursor above it in the mission control until an "x" appears) but in my case it does not work (i.e., no "x" pops up). I unchecked everything in the System Preferences related to spaces and logged out, to no avail.
Any hints?