O Firefox 57 é multithread?
Sim, e também é configurável.
You may see 3 or more processes running in the Task Manager
- one process for the main Firefox window (user interface)
- one or more processes for content threads set via "Options/Preferences -> General -> Performance" (dom.ipc.processCount), default in 57 is 4.
- one process for the compositor thread (Windows)
- one process for Quantum CSS (Stylo)
Fonte Por que o Firefox Quantum está executando 7 instâncias?