If this is happens to you, it may be caused by a jQuery library conflict. The testimonials PHP template directly includes jQuery and this may clash with the prototype library, we found that we could resolve the library conflict by placing good old:
In the file testimonial_advance.phtml just before document/ready, like this…
Adding this solved the problem for us.
testimonial_advance.phtml should be found in this folder:
However, it is not good magento practice to alter this version of the file, instead you should create a testimonials folder under:
Then copy testimonial_advance.phtml to this folder and edit it there. Remember to clear the magento cache when testing changes!