Is it possible to slow down Javascript Interpreter on purpose?

I want to make my browser to execute javascript code slower. Is there a Browser addon or something to do this?

Background: I want to demonstrate the impact of execution time on a given browser game. The speed of this game is only limited by the speed of the execution time of its code, just like in the good old MS-DOS Games. To show students the impact of such coding (depending on CPU cycles and not on time), it would be great if I could throttle down the execution speed of the code.

Any ideas?

Thanks!