When you hover over "Disable Media Viewer" in the footer of MV, a tooltip is shown: "Media Viewer will no longer be used to show images. To use it again, click on the "Expand view" button next to any image. Then click on "Enable Media Viewer"."
For "Enable Media Viewer": "Media Viewer will now be used to show images."
Either show these messages only after the user clicks the link to disable/enable MV, or rephrase them to make clear that they will only apply when the users clicks. Especially the "now" in the second tooltip is very misleading.