Theme's Customize page blinks on and off too fast to choose options.

When I try to customize the Twenty Fourteen theme using the Customize button, the Customize page loads but the preview window keeps opening and closing and the page resets, apparently saving itself (the Save button displays “Saved” instead of “Save”) over and over. This happens too quickly for me to change any options . . . much less, save them.

Bottom line, I can’t use the Customize feature to make any changes. How do I get past this problem?