Hi,
The tabs system doesn't need mootools. But yes, if you have a javascript error on the page, the javascript of the tabs system cannot be initialized and thus the tabs won't work.
squeezebox is the library used for the mootools modal popups. If you remove mootools from the page, the squeezebox library cannot work properly.
So the solution is either to keep mootools, or remove the popups.
For example, if you set the add to cart to display a popup notice when you click on the add to cart buttons, it will use the mootools modal popups and thus need squeezebox. Deactivate the popup notice on the add to cart buttons if you have them.
It could be something else, but since I don't know what you have on the page with that error I can't tell you.