According to How to Change Content Process Limit in Firefox Browser the default for the content process limit since FF 55 is 4 and this is also mentioned on Firefox's performance settings page.
Well, I'm running 56.0.2 (64-Bit) here and the value is set to 1 and I can't change it (the drop-down box is grayed out).
Starting FF in safe-mode does neither change the value nor activate the drop-down box.
There are three
dom.ipc.processCount[...] settings in about:config set to
1. Q1: Is this the place to change the setting if it is not changeable via the UI?
Q2: Why is it not changeable via the UI? Q3: How to fix this?