Is is possible to prevent OS X firmware password removal?
In a word, no.  If you are concerned with the contents of your machine being compromised should the machine be stolen a better bet may be to encrypt your drive with FileVault (assuming you are or intend to upgrade to using Lion).  Even if the firmware passwords was irreversible, it would not stop someone simply taking your disk out and reading another way.  The only benefit I can see is preventing a theif from being able to ever use the mcahine he just stole, but frankly this won't help stop your laptop from being stolen in the first place, although it probably would result in it getting binned if it was, rather than re-used and potentially identified at a later date via it's serial number etc.