Firefox

Install Firefox via these packages (adjust for your desired locale):

pacman -S firefox firefox-i18n-de

Wayland

To enable native Wayland rendering in Firefox set the following:

echo "MOZ_ENABLE_WAYLAND=1" >> /etc/environment
echo "MOZ_WEBRENDER=1" >> /etc/environment

Alternatively, navigate to about:config and set gfx.webrender.all to true to enable WebRender compositor.

Hardware Decoding

Utilizing GPU hardware accelerated decoding of video content results in smoother playback of HD/4K content, while reducing CPU load and power draw. Set the following in about:config to enable hardware accelerated video playback in Firefox:

Setting key	Value	Description
`media.ffmpeg.vaapi.enabled`	`true`	Enable VA-API usage
`media.ffvpx.enabled`	`false`	Disable internal VP8/9 software decoders
`media.rdd-vpx.enabled`	`false`	Disable codec sandbox for VP8/9
`media.navigator.mediadatadecoder_vpx_enabled`	`true`	Enable hardware encoding for WebRTC

To test if Firefox is actually using VA-API to decode video you can launch it with the following command:

MOZ_LOG="PlatformDecoderModule:5" firefox 2>&1 | grep 'VA-API'

If your log output reads something like the following video decoding via VA-API is working.

[Child 55975: MediaPDecoder #3]: D/PlatformDecoderModule VA-API Got one frame output with pts=135468000dts=135468000 duration=17000 opaque=-9223372036854775808
[Child 55975: MediaPDecoder #3]: D/PlatformDecoderModule Reusing VA-API DMABufSurface UID = 10

Plasma Integration

Control media playback from KDE

For better integration of Firefox into the KDE Plasma desktop, install the Plasma Integration add-on either via the Mozilla Add-on page or via AUR:

TIP: To prevent duplicate entries in the Media Player widget or tray icon, set media.hardwaremediakeys.enabled to false. This disables the media entry from Firefox and only uses the one from the Plasma integration add-on.

yay -S firefox-extension-plasma-integration

Make Firefox use KDE Dialogs

By default, Firefox uses GTK file and print dialogs, even on KDE. To change this to KDE native dialogs set one of the following: