The following post is insightful on working with Firefox profiles:

but I came across this issue and wanted to know if others have encountered it and have other solutions:

What Iíve noticed, at least for FF 3.6 profile manager is that there is no option to import and export an existing FF profile. So you can only create new ones and edit existing ones on your FF installation (i.e. existing profiles youíve set up on the machine).
As a hack, to do an import, Iíve create a dummy profile with the manager, then open FF with it, and exit FF. Then replace/overwrite content in that profile with profile to import. Then open FF again with that modified profile and make any additional changes as needed, then exit. Then can manually copy back that profile folder elsewhere as export step. This method allows you to update a FF profile created on another machine.

Is there any better method to do an import/export other than my hack? Or use newer version of FF?