MainThread unfamiliar process suddenly showing up 18.04

This morning, running top, I noticed a process I nave never seen before in my Ubuntu 18.04 laptop called MainThread, which was periodically using a lot of CPU . There was also an entry called Privileged Cont.

I recently installed nordvpn, but nordvpn support said the process is not theirs. Is this a new part of the operating system? Is it malware? It has never appeared in top on my laptop before, as far as I know.

Solution 1:

It is a change in recent firefox version (79+).

There is a bug about this.

Solution 2:

In addition to other answers there is a problem I encountered killing Firefox.

Previously I could usesudo killall firefox. Now that has no effect and pgrep firefox finds nothing.

For me to kill an unresponsive Firefox session I now need to use:

sudo killall /usr/lib/firefox/firefox

Note above problem isn't limited to Ubuntu 18.04 as I'm using Ubuntu 16.04.6 LTS.

Solution 3:

Today I also saw that process and when I executed the kill command, firefox it closed immediately. When I re-opened Firefox the process reappeared, but when I killed Firerox's WebExtensions process, MainThread significantly reduced memory usage.