An automator or script that will clear my Safari/Firefox

On Firefox, you can go to Options > Privacy > Always clear my private data when I close Firefox. You can specify which (or all) private data you want to delete.

So you may only need a script for Safari.

 

On Safari, all you need to do is click Safari > Reset Safari

 

Clear Safari history and topsites with automator - 2010

The way I do this is to use automator to find the files history.plist and toplist.plist and move them both to the trash. The files are in the Library > Safari. Be sure to close Safari before you do this so when it is next launched the history and topsite folders will be clear.