Very High Single Core CPU Usage

[ArtificialAmateur]

Distribution (run cat /etc/os-release):

NAME="Pop!_OS"
VERSION="18.10"
ID=ubuntu
ID_LIKE=debian
PRETTY_NAME="Pop!_OS 18.10"
VERSION_ID="18.10"
HOME_URL="https://system76.com/pop"
SUPPORT_URL="http://support.system76.com"
BUG_REPORT_URL="https://github.com/pop-os/pop/issues"
PRIVACY_POLICY_URL="https://system76.com/privacy"
VERSION_CODENAME=cosmic
UBUNTU_CODENAME=cosmic

Related Application and/or Package Version (run apt policy $PACKAGE NAME):

xorg:
  Installed: 1:7.7+19ubuntu8
  Candidate: 1:7.7+19ubuntu8
  Version table:
 *** 1:7.7+19ubuntu8 500
        500 http://us.archive.ubuntu.com/ubuntu cosmic/main amd64 Packages
        100 /var/lib/dpkg/status

Issue/Bug Description: When I open a Youtube video on Firefox on fullscreen in its own workspace one of my CPU Cores will jump up to 100% utilization, causing the fans to ramp up, temperature to skyrocket, and whole DE to lag.

Steps to reproduce (if you know):

1. Open firefox
2. Open a youtube video
3. Put video in full-screen
4. Press play
5. Expect major slowdown

Expected behavior: To spread out core utilization without turning my laptop into a burning jet engine.

Other Notes:

• htop shows the program that jumps up to 95% CPU Usage to be: /usr/lib/xorg/Xorg vt2 -displayfd 3 -auth /run/user/1000/gdm/Xauthority -background none -noreset -keeptty -verbose 3

• Here are my specs

• Here are my system resources when I play the video.

• Here are my system resources after I paused the video.

[mmstick]

Does the same happen in Chromium?

[ArtificialAmateur]

It does not... Seems this is more of a firefox issue?

[mmstick]

Highly likely. Firefox has hardware acceleration issues on Linux, sadly. Chrome often fares much better in the HW accel department.