The iMacros Enterprise Edition works currently only on Windows OS, however you can use popular "Mac" languages such as Perl, Python, PHP or Ruby to script it on Windows. Of course, iMacros also runs well in any virtual machine that you can host on your Mac. Plus, you can already use iMacros for Firefox on the Mac for free and control the browser via the command line interface:
Plans for a native version of the iMacros Scripting Interface for Mac OS X have been suspended indefinitely.
Please cast your vote to express interest in having this effort resumed.