Mask == lightbox == that grey thing in the background you sometimes get (for modal dialogues only) Check various Moodle dialogues to make sure that they do not appear behind their masks: activity chooser qbank chooser (2.7 only) editpdf block mover (the popup version) Check there are no errors when opening various non-modal dialogues: help popups Un-tgz the attached file (45359.tgz) into your root directory Point your browser at http://path/to/moodle/45359 Click on the Confirm that the help dialogue is shown correctly without a mask Close it, re-open, and confirm again Close it Click on the 'Click me' text Confirm that the dialogue is shown correctly in front of it's mask Click on the icon in it Confirm that the mask is still shown behind both dialogues Confirm that the help dialogue is in front Close it with it's [X] Re-open, and re-confirm Close both dialogues Re-open the dialogue Reconfirm Refresh the page Open the popup (not the help) immediately this time Repeat previous set of tests on this dialogue again Close and check the help button on the page itself again