Firefox

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

pacman -S firefox firefox-i18n-de

Wayland

Wayland is not yet the default display manager for Firefox (it falls back to XWayland on Wayland). To force Firefox to use Wayland you can set the MOZ_ENABLE_WAYLAND environment variable to 1. Use user specific systemd environment variable configs to set it:

echo "MOZ_ENABLE_WAYLAND=1" >> ~/.config/environment.d/moz_wayland.conf

Media Playback

Autoplay in background

Firefox prevents autoplay for media of tabs that aren't currently active, which causes apps like Plex to take very long to skip to the next track after the current one has ended. The following setting in about:config can be used to disable this behavior:

Setting key	Value	Description
`media.block-autoplay-until-in-foreground`	`false`	Enable autoplay when tab is not currently active

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 (important to save on battery on laptops).

To ensure Firefox uses hardware decoding ensure the following:

The necessary VA-API drivers are installed (see: Graphics Cards)
Navigate to about:support and ensure that under Compositing it says WebRender (WebRender Software will not work)
Navigate to about:config and set media.ffmpeg.vaapi.enabled to true
If running Wayland, enable Wayland mode in Firefox (see above)

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

MOZ_LOG="FFmpegVideo: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

KDE 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: