A number of people are experiencing this issue. If Firebug is enabled it will break before displaying tooltips due to an error in the script.

A useful thread where the issue is broken down can be found here:

http://flowplayer.org/tools/forum/30/28298

From user Zappo:

"In the jQuery line 2447: if ( !handler.guid )
the handler is not optional.
However, searching through the jQuery tools code (v.1.1.2), the third variable (handler) is not always passed!"