When you are in the Xena Visual Spreadsheet mousing over any data will trigger a tooltip to show up at the top of the view. Sometimes you might want to copy the sample id in the tooltip, or click on the link to take you to the UCSC Genome Browser, where you can view more information. You need to first freeze the tooltip.
To freeze the tooltip, you need to "Alt-click", i.e. hold on the ALT key on your computer and at the same time click the left mouse button.
To unfreeze the tooltip, click on the close (X) icon.