A B737-300 WAS DISPATCHED IN NON COMPLIANCE WITH THE APU FIRE WARNING SYS DEFERRED BUT NOT IN ACCORDANCE WITH THE MEL.

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ON JUN/FRI/02 AT ZZZ INTL ARPT; I WAS WORKING AS AN AVIONICS TECHNICIAN AT THE TERMINAL FOR X AIRLINES. ACFT X WAS 10 MINS FROM PUSHBACK WHEN THE CREW RPTED THE APU FIRE TEST INDICATIONS WERE INOP. THE CREW WAS AGREEABLE TO TAKING THE ACFT WITH THE APU DEFERRED INOP. APPROX 1 MONTH AGO; THE ENTIRE MEL (ON-LINE) SYS WAS UPDATED AND REFORMATTED. NO ADVANCE NOTICE WAS GIVEN; NOR WAS ANY TRAINING/INSTRUCTION MADE AVAILABLE TO ANY OF US WORKING THE LINE IN ZZZ. AFTER A BRIEF SEARCH OF THE CHAPTER 26 MEL; I OBTAINED PERMISSION FROM MY SUPVR AND DISPATCH TO USE CHAPTER 49 MEL 4900E. THE APPROPRIATE CIRCUIT BREAKERS WERE COLLARED; PLACARDS INSTALLED; AND WRITE-UP ENTRIES MADE TO REFLECT THE APU SYS INOP/DEFERRAL. THE ACFT WAS DISPATCHED. 2 DAYS LATER; (AFTER SEVERAL INDIVIDUALS TROUBLESHOOTING WITHOUT SUCCESS); ACFT X RECEIVED AN APU FIRE WARNING ON FINAL APCH. THE FIRE DEPT WAS ALERTED AND TRUCKS FOLLOWED THE ACFT TO THE GATE WHERE IT WAS INSPECTED. NO EVIDENCE OF FIRE OR OVERHEATING WAS FOUND. AT THIS TIME IT WAS BROUGHT TO MY ATTN THAT MEL 2611B FOR THE FIRE LOOP SHOULD HAVE BEEN USED BY ME AT THE SAME TIME THAT I DEFERRED THE APU ON JUN/FRI/02. THE FACT THAT MY SUPVR AND DISPATCHER AGREED WITH MY ORIGINAL DEFERRAL DOES NOT EXCUSE ME FROM THE OVERSIGHT OF ALSO RENDERING INOP THE APU FIRE LOOP. I DO NOT KNOW WHAT WAS DONE TO THE ACFT APU FIRE DETECTION SYS DURING TROUBLESHOOTING ON JUN/FRI/02 AND JUN/SAT/02; HOWEVER; I TAKE THE RESPONSIBILITY FOR NOT BEING AWARE OF MEL 2611B WHICH WOULD HAVE PREVENTED THE FALSE APU FIRE WARNING AND ALL SUBSEQUENT EVENTS. THE PROBS IN THIS EVENT WERE MY LACK OF FAMILIARITY WITH THE NEW MEL FORMAT; AND NO DISAGREEMENT WITH MY DEFERRAL FROM DISPATCH; MY SUPVR OR THE GATE MECH. THIS DEFERRAL ON ACFT X APU SYS WAS UPDATED TO REFLECT MEL 2611B ON JUN/SUN/02.