The DLL with name iimfirefoxconnector.dll is the Firefox part of the iMacros Scripting Interface. It receives the commands from iimInit, iimPlay etc.
Since Firefox 6 and iMacros for Firefox 18.104.22.168 this DLL is no longer included with the iMacros for Firefox installer, but is shipped directly with iMacros Enterprise Edition 7.5 and later.
If you have an earlier iMacros Edition, please download this DLL and simply place it in the iMacros installation folder, alongside iMacros.exe. The path is usually C:\Program Files (x86)\Ipswitch\iMacros (64bit systems) or C:\Program Files\Ipswitch\iMacros (32bit systems)