If you do not use Drupal, you may have to download and install jQuery. See jQuery for people not using Drupal - Installation and getting started.
Read about the flashy
.hover() function in jQuery hover.
Yahoo developed a user interface library, YUI, that is many times larger than jQuery, much harder to use, and is generally a pain compared to jQuery. YUI has enough errors, or inconsistencies between code and documentation, that you are unlikely to get to a point where you will run into debug problems with Firebug.
Use jQuery but push the developers to clean up the code using the Firebird diagnostics and Firebug.