Script causing browser to run slow

[Sandie]

I keep getting the message

A script on this page is causing your web browser to run slowly.
If it continues to run your computer might become unresponsive.
Stop running this script? check yes or no

This is happening (or at least the only place I have seen it) just on Facebook. I honestly dont understand what it means, and is there anything I can do about it? Thanks for any help. Sandie

 

[elfsun]

I guess it's related with your security setting