Xorg – change display resolution on AMD GPU, Debian

When I tried to create a new mode in Xorg (via xrandr --newmode), I get the following error:
Failed to get size of gamma for output default
The solution turned out to be simple: I just had to install the firmware-linux-nonfree package and reboot the PC.
So, here is the complete resolution change process:

  1. cvt <width> <height> <refresh rate>, output may be something like this:
    # 1920x1080 59.96 Hz (CVT 2.07M9) hsync: 67.16 kHz; pclk: 173.00 MHz Modeline "1920x1080_60.00" 173.00 1920 2048 2248 2576 1080 1083 1088 1120 -hsync +vsync
  2. xrandr --newmode "1920x1080_60.00" 173.00 1920 2048 2248 2576 1080 1083 1088 1120 -hsync +vsync
  3. xrandr --addmode <OUTPUT> 1920x1080_60.00, OUTPUT can be extracted from xrandr output. It can be something like DVI-0, HDMI-0 etc
  4. To apply new mode that you created execute xrandr --output <OUTPUT> --mode 1920x1080_60.00

After that, the screen resolution will change to the one you specified.

Firefox useful settings

You can found hidden config on about:config

  • layers.acceleration.force-enabled set to true, if your screen flickering when you scrolling or watching videos
  • layout.css.devPixelsPerPx can control browser scale with this param. Very useful for users which have HiDPI screens!

Update 19.06.20/20.06.20:

  • browser.display.focus_ring_width set to 0 to remove ugly dotted borders around the links
  • gfx.webrender.all set to true to enable WebRender
  • browser.tabs.tabMinWidth reduce to fit more tabs (like in Chromium)