--- a/b2g/app/b2g.js
+++ b/b2g/app/b2g.js
@@ -871,16 +871,18 @@ pref("webgl.can-lose-context-in-foregrou
 pref("memory_info_dumper.watch_fifo.enabled", true);
 pref("memory_info_dumper.watch_fifo.directory", "/data/local");
 
 // See ua-update.json.in for the packaged UA override list
 pref("general.useragent.updates.enabled", true);
 pref("general.useragent.updates.url", "https://dynamicua.cdn.mozilla.net/0/%APP_ID%");
 pref("general.useragent.updates.interval", 604800); // 1 week
 pref("general.useragent.updates.retry", 86400); // 1 day
+// Device ID can be composed of letter, numbers, hyphen ("-") and dot (".")
+pref("general.useragent.device_id", "");
 
 // Make <audio> and <video> talk to the AudioChannelService.
 pref("media.useAudioChannelService", true);
 
 pref("b2g.version", @MOZ_B2G_VERSION@);
 pref("b2g.osName", @MOZ_B2G_OS_NAME@);
 
 // Disable console buffering to save memory.

--- a/netwerk/protocol/http/nsHttpHandler.cpp
+++ b/netwerk/protocol/http/nsHttpHandler.cpp
@@ -611,16 +611,17 @@ nsHttpHandler::BuildUserAgent()
                            mOscpu.Length() +
                            mMisc.Length() +
                            mProduct.Length() +
                            mProductSub.Length() +
                            mAppName.Length() +
                            mAppVersion.Length() +
                            mCompatFirefox.Length() +
                            mCompatDevice.Length() +
+                           mDeviceModelId.Length() +
                            13);
 
     // Application portion
     mUserAgent.Assign(mLegacyAppName);
     mUserAgent += '/';
     mUserAgent += mLegacyAppVersion;
     mUserAgent += ' ';
 
@@ -635,16 +636,20 @@ nsHttpHandler::BuildUserAgent()
     if (!mCompatDevice.IsEmpty()) {
         mUserAgent += mCompatDevice;
         mUserAgent.AppendLiteral("; ");
     }
     else if (!mOscpu.IsEmpty()) {
       mUserAgent += mOscpu;
       mUserAgent.AppendLiteral("; ");
     }
+    if (!mDeviceModelId.IsEmpty()) {
+        mUserAgent += mDeviceModelId;
+        mUserAgent.AppendLiteral("; ");
+    }
     mUserAgent += mMisc;
     mUserAgent += ')';
 
     // Product portion
     mUserAgent += ' ';
     mUserAgent += mProduct;
     mUserAgent += '/';
     mUserAgent += mProductSub;
@@ -698,16 +703,41 @@ nsHttpHandler::InitUserAgentComponents()
     bool isTablet;
     nsresult rv = infoService->GetPropertyAsBool(NS_LITERAL_STRING("tablet"), &isTablet);
     if (NS_SUCCEEDED(rv) && isTablet)
         mCompatDevice.AssignLiteral("Tablet");
     else
         mCompatDevice.AssignLiteral("Mobile");
 #endif
 
+#if defined(MOZ_WIDGET_GONK)
+    // Device model identifier should be a simple token, which can be composed
+    // of letters, numbers, hyphen ("-") and dot (".").
+    // Any other characters means the identifier is invalid and ignored.
+    nsCString deviceId;
+    rv = Preferences::GetCString("general.useragent.device_id", &deviceId);
+    if (NS_SUCCEEDED(rv)) {
+        bool valid = true;
+        deviceId.Trim(" ", true, true);
+        for (int i = 0; i < deviceId.Length(); i++) {
+            char c = deviceId.CharAt(i);
+            if (!(isalnum(c) || c == '-' || c == '.')) {
+                valid = false;
+                break;
+            }
+        }
+        if (valid) {
+            mDeviceModelId = deviceId;
+        } else {
+            LOG(("nsHttpHandler: Ignore invalid device ID: [%s]\n",
+                  deviceId.get()));
+        }
+    }
+#endif
+
 #ifndef MOZ_UA_OS_AGNOSTIC
     // Gather OS/CPU.
 #if defined(XP_WIN)
     OSVERSIONINFO info = { sizeof(OSVERSIONINFO) };
 #pragma warning(push)
 #pragma warning(disable:4996)
     if (GetVersionEx(&info)) {
 #pragma warning(pop)

--- a/netwerk/protocol/http/nsHttpHandler.h
+++ b/netwerk/protocol/http/nsHttpHandler.h
@@ -427,16 +427,17 @@ private:
     nsCString      mMisc;
     nsCString      mProduct;
     nsXPIDLCString mProductSub;
     nsXPIDLCString mAppName;
     nsXPIDLCString mAppVersion;
     nsCString      mCompatFirefox;
     bool           mCompatFirefoxEnabled;
     nsXPIDLCString mCompatDevice;
+    nsCString      mDeviceModelId;
 
     nsCString      mUserAgent;
     nsXPIDLCString mUserAgentOverride;
     bool           mUserAgentIsDirty; // true if mUserAgent should be rebuilt
 
     bool           mUseCache;
 
     bool           mPromptTempRedirect;