Step 3. Once in download mode, connect your Galaxy S3 to your Mac OSX computer/laptop using a microUSB cable.
Step 4. Download GalaxyS3RootMac.zip, you will find a folder called GalaxyS3RootMac in your Downloads directory with all the files you need for rooting your Galaxy S3.
Step 5. Double-click on the file heimdall-suite-1.3.2-mac.dmg to install Heimdall. Reboot your computer after installation is complete.
Step 6. You should now find Heimdall-frontend app in your Application folder, double-click on it to run. Choose “Flash” then “Browse” and choose the file “s3pit.pit” in GalaxyS3RootMac folder.
Step 7. Click on “Add”, change Partition Name to “RECOVERY”. Then choose “Browse” and select the file “recovery.img” in GalaxyS3RootMac folder.