--- a/dom/media/CubebUtils.cpp
+++ b/dom/media/CubebUtils.cpp
@@ -28,16 +28,19 @@
 #ifdef MOZ_WIDGET_ANDROID
 #include "GeneratedJNIWrappers.h"
 #endif
 
 #define PREF_VOLUME_SCALE "media.volume_scale"
 #define PREF_CUBEB_BACKEND "media.cubeb.backend"
 #define PREF_CUBEB_LATENCY_PLAYBACK "media.cubeb_latency_playback_ms"
 #define PREF_CUBEB_LATENCY_MSG "media.cubeb_latency_msg_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 "media.cubeb.logging_level"
 #define PREF_CUBEB_SANDBOX "media.cubeb.sandbox"
 
 #define MASK_MONO       (1 << AudioConfig::CHANNEL_MONO)
 #define MASK_MONO_LFE   (MASK_MONO | (1 << AudioConfig::CHANNEL_LFE))
 #define MASK_STEREO     ((1 << AudioConfig::CHANNEL_LEFT) | (1 << AudioConfig::CHANNEL_RIGHT))
 #define MASK_STEREO_LFE (MASK_STEREO | (1 << AudioConfig::CHANNEL_LFE))
 #define MASK_3F         (MASK_STEREO | (1 << AudioConfig::CHANNEL_CENTER))
@@ -117,16 +120,20 @@ enum class CubebState {
   Uninitialized = 0,
   Initialized,
   Shutdown
 } sCubebState = CubebState::Uninitialized;
 cubeb* sCubebContext;
 double sVolumeScale = 1.0;
 uint32_t sCubebPlaybackLatencyInMilliseconds = 100;
 uint32_t sCubebMSGLatencyInFrames = 512;
+// If sCubebForcedSampleRate is zero, PreferredSampleRate will return the
+// preferred sample-rate for the audio backend in use. Otherwise, it will be
+// used as the preferred sample-rate.
+uint32_t sCubebForcedSampleRate = 0;
 bool sCubebPlaybackLatencyPrefSet = false;
 bool sCubebMSGLatencyPrefSet = false;
 bool sAudioStreamInitEverSucceeded = false;
 #ifdef MOZ_CUBEB_REMOTING
 bool sCubebSandbox;
 #endif
 StaticAutoPtr<char> sBrandName;
 StaticAutoPtr<char> sCubebBackendName;
@@ -232,16 +239,19 @@ void PrefChanged(const char* aPref, void
     sCubebMSGLatencyPrefSet = Preferences::HasUserValue(aPref);
     uint32_t value = Preferences::GetUint(aPref, CUBEB_NORMAL_LATENCY_FRAMES);
     StaticMutexAutoLock lock(sMutex);
     // 128 is the block size for the Web Audio API, which limits how low the
     // latency can be here.
     // We don't want to limit the upper limit too much, so that people can
     // experiment.
     sCubebMSGLatencyInFrames = std::min<uint32_t>(std::max<uint32_t>(value, 128), 1e6);
+  } else if (strcmp(aPref, PREF_CUBEB_FORCE_SAMPLE_RATE) == 0) {
+    StaticMutexAutoLock lock(sMutex);
+    sCubebForcedSampleRate = Preferences::GetUint(aPref);
   } else if (strcmp(aPref, PREF_CUBEB_LOGGING_LEVEL) == 0) {
     nsAutoCString value;
     Preferences::GetCString(aPref, value);
     LogModule* cubebLog = LogModule::Get("cubeb");
     if (value.EqualsLiteral("verbose")) {
       cubeb_set_log_callback(CUBEB_LOG_VERBOSE, CubebLogCallback);
       cubebLog->SetLevel(LogLevel::Verbose);
     } else if (value.EqualsLiteral("normal")) {
@@ -318,16 +328,19 @@ bool InitPreferredSampleRate()
   }
 #endif
   MOZ_ASSERT(sPreferredSampleRate);
   return true;
 }
 
 uint32_t PreferredSampleRate()
 {
+  if (sCubebForcedSampleRate) {
+    return sCubebForcedSampleRate;
+  }
   if (!InitPreferredSampleRate()) {
     return 44100;
   }
   MOZ_ASSERT(sPreferredSampleRate);
   return sPreferredSampleRate;
 }
 
 bool InitPreferredChannelLayout()
@@ -558,16 +571,17 @@ uint32_t GetCubebMSGLatencyInFrames(cube
 #endif
 }
 
 void InitLibrary()
 {
   Preferences::RegisterCallbackAndCall(PrefChanged, PREF_VOLUME_SCALE);
   Preferences::RegisterCallbackAndCall(PrefChanged, PREF_CUBEB_LATENCY_PLAYBACK);
   Preferences::RegisterCallbackAndCall(PrefChanged, PREF_CUBEB_LATENCY_MSG);
+  Preferences::RegisterCallback(PrefChanged, PREF_CUBEB_FORCE_SAMPLE_RATE);
   Preferences::RegisterCallbackAndCall(PrefChanged, PREF_CUBEB_BACKEND);
   Preferences::RegisterCallbackAndCall(PrefChanged, PREF_CUBEB_SANDBOX);
   if (MOZ_LOG_TEST(gCubebLog, LogLevel::Verbose)) {
     cubeb_set_log_callback(CUBEB_LOG_VERBOSE, CubebLogCallback);
   } else if (MOZ_LOG_TEST(gCubebLog, LogLevel::Error)) {
     cubeb_set_log_callback(CUBEB_LOG_NORMAL, CubebLogCallback);
   }
   // We don't want to call the callback on startup, because the pref is the
@@ -587,16 +601,17 @@ void InitLibrary()
 }
 
 void ShutdownLibrary()
 {
   Preferences::UnregisterCallback(PrefChanged, PREF_VOLUME_SCALE);
   Preferences::UnregisterCallback(PrefChanged, PREF_CUBEB_SANDBOX);
   Preferences::UnregisterCallback(PrefChanged, PREF_CUBEB_BACKEND);
   Preferences::UnregisterCallback(PrefChanged, PREF_CUBEB_LATENCY_PLAYBACK);
+  Preferences::UnregisterCallback(PrefChanged, PREF_CUBEB_FORCE_SAMPLE_RATE);
   Preferences::UnregisterCallback(PrefChanged, PREF_CUBEB_LATENCY_MSG);
   Preferences::UnregisterCallback(PrefChanged, PREF_CUBEB_LOGGING_LEVEL);
 
   StaticMutexAutoLock lock(sMutex);
   if (sCubebContext) {
     cubeb_destroy(sCubebContext);
     sCubebContext = nullptr;
   }

--- a/dom/media/tests/mochitest/mochitest.ini
+++ b/dom/media/tests/mochitest/mochitest.ini
@@ -324,8 +324,9 @@ skip-if = (android_version == '18') # an
 [test_peerConnection_bug1227781.html]
 [test_peerConnection_stats.html]
 skip-if = toolkit == 'android' # android(Bug 1189784, timeouts on 4.3 emulator, Bug 1373858)
 [test_peerConnection_sender_and_receiver_stats.html]
 skip-if = (android_version == '18') # android(Bug 1189784, timeouts on 4.3 emulator)
 [test_peerConnection_verifyDescriptions.html]
 skip-if = (android_version == '18')
 [test_fingerprinting_resistance.html]
+[test_forceSampleRate.html]

new file mode 100644
--- /dev/null
+++ b/dom/media/tests/mochitest/test_forceSampleRate.html
@@ -0,0 +1,23 @@
+<!DOCTYPE HTML>
+<html>
+<head>
+  <title>Test the pref media.cubeb.force_sample_rate</title>
+  <script type="text/javascript" src="/MochiKit/MochiKit.js"></script>
+  <script type="text/javascript" src="/tests/SimpleTest/SimpleTest.js"></script>
+  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css" />
+</head>
+<body>
+<script class="testbody" type="text/javascript">
+const WEIRD_SAMPLE_RATE = 44101;
+
+SimpleTest.waitForExplicitFinish();
+SpecialPowers.pushPrefEnv({"set": [
+  ["media.cubeb.force_sample_rate", WEIRD_SAMPLE_RATE]
+]}).then(function() {
+  var ac = new AudioContext();
+  is(ac.sampleRate, WEIRD_SAMPLE_RATE, "Forced sample-rate set successfully.");
+  SimpleTest.finish();
+});
+</script>
+</pre>
+</body>