script in movie error

One of the ads on ATS has been popping up VERY FREQUENTLY

that brings about an error that says

a script in the movie is causing flash player 9 to run slowly, affecting system performance.

Mozilla Locks up, and i have to close it and start over.

Any ideas:

A.) If the ad can be singled out and removed
B.) If im doing something wrong?

Windows Vista
with latest Mozilla Firefox browser, all updated.