Pernosco was designed from the start to support debugging of multiprocess recordings. All debugging operations operate across all processes by default.
Multiprocess applications such as Firefox share memory between processes and these memory regions are typically mapped at different addresses in each process. Accurately tracking data flow between processes requires the debugger to understand how the virtual address space of each process maps onto "physical memory". Pernosco does this, and therefore tracing the dataflow to an address X in one process may reveal it was written at address Y in another process. (This can also happen within a single process when it has multiple shared mappings of the same page(s).)