firefox.exe is a part of the Mozilla Internet browsing suite, an alternative browsing application which offers a surfing alternative. This is the main process belonging to this browser and termination will cause the loss of any web pages loaded.
Non-system processes like firefox.exe originate from software you installed on your system. Since most applications store data in your system's registry, it is likely that your registry has suffered fragmentation and accumulated invalid entries which can affect your PC's performance. It is recommended that you check your registry to identify slowdown issues