The documentation implies that you can run concurrent iMacros by starting Firefox sessions under different profiles. I have tried this, but if I run Firefox from the command line it only takes note of the -P (profile) option if I am also specifying -no-remote (start in a new process). the problem is that to run an iMacro from the command line you have to start a firefox session first, then wait briefly before making the actual firefox call to your iMacro. So I can start a number of separate Firefox sessions under different profiles OK, but when I try to call my iMacros they might go to any of the sessions, and they just end up all hanging.

If I start my Firefox sessions then go into them manually, I can start the iMacros one iMacro in each and they run fine concurrently.