Add the following to the end of you php.ini file in MAMP
[xdebug]
zend_extension="/Applications/MAMP/bin/php/php5.3.14/lib/php/extensions/no-debug-non-zts-20090626/xdebug.so"
xdebug.remote_enable=1
xdebug.profiler_enable_trigger=1
xdebug.remote_host=localhost
xdebug.remote_port=9000
xdebug.remote_handler=dbgp