How to change PreferredSampleRate in Firefox's about:config

dummy@example.com (igorzwx) — Thu, 23 Oct 2025 03:00:00 +0000

The top secret settings in Firefox's about:config are invisible. For example:

// Allows to get something non-default for the preferred sample-rate
media.cubeb.force_sample_rate

media.cubeb.backend
media.cubeb.output_device

_https://searchfox.org/firefox-main/source/dom/media/CubebUtils.cpp

#define PREF_VOLUME_SCALE "media.volume_scale"
#define PREF_CUBEB_BACKEND "media.cubeb.backend"
#define PREF_CUBEB_OUTPUT_DEVICE "media.cubeb.output_device"
#define PREF_CUBEB_LATENCY_PLAYBACK "media.cubeb_latency_playback_ms"
#define PREF_CUBEB_LATENCY_MTG "media.cubeb_latency_mtg_frames"
// Allows to get something non-default for the preferred sample-rate, to allow
// troubleshooting in the field and testing.
#define PREF_CUBEB_FORCE_SAMPLE_RATE "media.cubeb.force_sample_rate"
#define PREF_CUBEB_LOGGING_LEVEL "logging.cubeb"
// Hidden pref used by tests to force failure to obtain cubeb context

Open a new tab in Firefox. Type about:config in the address bar.
Type into "Search preference name"

media.cubeb.force_sample_rate

Select "Number"
Press "+"
Type "48000", then Enter

You have a new entry in Firefox's "hidden preferences":

media.cubeb.force_sample_rate        48000

Restart Firefox. Type about:support in the address bar.

Name 	Firefox
Version 	140.4.0esr
...
Media
Audio Backend	alsa
Max Channels	10000
Preferred Sample Rate	48000

Reference media files:
Hi-Res Music 32 Bit - Greatest Audiophile Collection - Natural Beat Records
_https://rutube.ru/video/b54c962301787eb1f2758ac8ba97f5bf/
Best Audiophile Vocal 24 bit - Hi-Res Music 2025 - Audiophile Voices
_https://www.youtube.com/watch?v=uO6jfQ5tQHM
_https://youtu.be/uO6jfQ5tQHM
$ youtube-dl -F "https://youtu.be/uO6jfQ5tQHM" | grep "audio only"
249          webm       audio only audio_quality_low   54k , webm_dash container, opus  (48000Hz), 30.39MiB
250          webm       audio only audio_quality_low   71k , webm_dash container, opus  (48000Hz), 39.87MiB
140          m4a        audio only audio_quality_medium  129k , m4a_dash container, mp4a.40.2 (44100Hz), 72.39MiB
251          webm       audio only audio_quality_medium  137k , webm_dash container, opus  (48000Hz), 76.97MiB

$ firefox 2>&1 youtube.com/watch?v=uO6jfQ5tQHM
Input:  44100 Hz, 2 ch, 's32_le' (0xa): dummy = 0, period = 1764
Output: 48000 Hz, 2 ch, 's16_le' (0x2): dummy = 0, period = 1920
Rates:  44100 --> 48000 (J: 0.00%, T: FFT, W: Vorbis)
Ok.

Input:  44100 Hz, 2 ch, 's32_le' (0xa): dummy = 0, period = 1764
Output: 48000 Hz, 2 ch, 's16_le' (0x2): dummy = 0, period = 1920
Rates:  44100 --> 48000 (J: 0.00%, T: FFT, W: Vorbis)
Ok.

Input:  48000 Hz, 2 ch, 's32_le' (0xa): dummy = 0, period = 1920
Output: 48000 Hz, 2 ch, 's16_le' (0x2): dummy = 0, period = 1920
Rates:  48000 --> 48000 (J: 0.00%, T: None, W: Planar)
Ok.

Input:  44100 Hz, 2 ch, 's32_le' (0xa): dummy = 0, period = 1764
Output: 48000 Hz, 2 ch, 's16_le' (0x2): dummy = 0, period = 1920
Rates:  44100 --> 48000 (J: 0.00%, T: FFT, W: Vorbis)
Ok.

$ firefox 2>&1 rutube.ru/video/b54c962301787eb1f2758ac8ba97f5bf
Input:  44100 Hz, 2 ch, 's32_le' (0xa): dummy = 0, period = 1764
Output: 48000 Hz, 2 ch, 's16_le' (0x2): dummy = 0, period = 1920
Rates:  44100 --> 48000 (J: 0.00%, T: FFT, W: Vorbis)
Ok.

The same is for PreferredSampleRate = 44100
It does not change Firefox's playback with ALSA.
You may test it with apulse

apulse firefox 2>&1

What has changed is that you can now see Preferred Sample Rate 48000 in about:support

The statement "The deaf may try a blind test. The blind may try a deaf test" is a philosophical observation about perspective, not a literal one. It points to the idea that people with different life experiences and challenges can gain new understanding by experiencing things from another's point of view.

Dev1 Galaxy Forum / How to change PreferredSampleRate in Firefox's about:config

How to change PreferredSampleRate in Firefox's about:config

Reference media files: