--- a/extensions/universalchardet/src/base/CharDistribution.cpp
+++ b/extensions/universalchardet/src/base/CharDistribution.cpp
@@ -44,22 +44,23 @@
 #include "GB2312Freq.tab"
 
 #define SURE_YES 0.99f
 #define SURE_NO  0.01f
 
 #define MINIMUM_DATA_THRESHOLD  4
 
 //return confidence base on received data
-float CharDistributionAnalysis::GetConfidence()
+float CharDistributionAnalysis::GetConfidence(PRBool aIsPreferredLanguage)
 { 
   //if we didn't receive any character in our consideration range, or the
   // number of frequent characters is below the minimum threshold, return
   // negative answer
-  if (mTotalChars <= 0 || mFreqChars <= MINIMUM_DATA_THRESHOLD)
+  if (mTotalChars <= 0 ||
+      !aIsPreferredLanguage && mFreqChars <= MINIMUM_DATA_THRESHOLD)
     return SURE_NO;
 
   if (mTotalChars != mFreqChars) {
     float r = mFreqChars / ((mTotalChars - mFreqChars) * mTypicalDistributionRatio);
 
     if (r < SURE_YES)
       return r;
   }

--- a/extensions/universalchardet/src/base/CharDistribution.h
+++ b/extensions/universalchardet/src/base/CharDistribution.h
@@ -66,17 +66,17 @@ public:
       {
         if (512 > mCharToFreqOrder[order])
           mFreqChars++;
       }
     }
   }
 
   //return confidence base on existing data
-  float GetConfidence();
+  float GetConfidence(PRBool aIsPreferredLanguage);
 
   //Reset analyser, clear any state 
   void      Reset(void) 
   {
     mDone = PR_FALSE;
     mTotalChars = 0;
     mFreqChars = 0;
   }

--- a/extensions/universalchardet/src/base/JpCntx.cpp
+++ b/extensions/universalchardet/src/base/JpCntx.cpp
@@ -176,20 +176,20 @@ void JapaneseContextAnalysis::Reset(void
   for (PRUint32 i = 0; i < NUM_OF_CATEGORY; i++)
     mRelSample[i] = 0;
   mNeedToSkipCharNum = 0;
   mLastCharOrder = -1;
   mDone = PR_FALSE;
 }
 #define DONT_KNOW (float)-1
 
-float  JapaneseContextAnalysis::GetConfidence()
+float  JapaneseContextAnalysis::GetConfidence(PRBool aIsPreferredLanguage)
 {
   //This is just one way to calculate confidence. It works well for me.
-  if (mTotalRel > MINIMUM_DATA_THRESHOLD)
+  if (aIsPreferredLanguage || mTotalRel > MINIMUM_DATA_THRESHOLD)
     return ((float)(mTotalRel - mRelSample[0]))/mTotalRel;
   else 
     return (float)DONT_KNOW;
 }
 
 
 PRInt32 SJISContextAnalysis::GetOrder(const char* str, PRUint32 *charLen)
 {

--- a/extensions/universalchardet/src/base/JpCntx.h
+++ b/extensions/universalchardet/src/base/JpCntx.h
@@ -69,17 +69,17 @@ public:
     {
       mTotalRel++;
       //count this sequence to its category counter
       mRelSample[jp2CharContext[mLastCharOrder][order]]++;
     }
     mLastCharOrder = order;
   }
 
-  float GetConfidence();
+  float GetConfidence(PRBool aIsPreferredLanguage);
   void      Reset(void);
   void      SetOpion(){}
   PRBool GotEnoughData() {return mTotalRel > ENOUGH_REL_THRESHOLD;}
 
 protected:
   virtual PRInt32 GetOrder(const char* str, PRUint32 *charLen) = 0;
   virtual PRInt32 GetOrder(const char* str) = 0;
 

--- a/extensions/universalchardet/src/base/nsBig5Prober.cpp
+++ b/extensions/universalchardet/src/base/nsBig5Prober.cpp
@@ -76,13 +76,13 @@ nsProbingState nsBig5Prober::HandleData(
     if (mDistributionAnalyser.GotEnoughData() && GetConfidence() > SHORTCUT_THRESHOLD)
       mState = eFoundIt;
 
   return mState;
 }
 
 float nsBig5Prober::GetConfidence(void)
 {
-  float distribCf = mDistributionAnalyser.GetConfidence();
+  float distribCf = mDistributionAnalyser.GetConfidence(mIsPreferredLanguage);
 
   return (float)distribCf;
 }
 

--- a/extensions/universalchardet/src/base/nsBig5Prober.h
+++ b/extensions/universalchardet/src/base/nsBig5Prober.h
@@ -39,18 +39,20 @@
 #define nsBig5Prober_h__
 
 #include "nsCharSetProber.h"
 #include "nsCodingStateMachine.h"
 #include "CharDistribution.h"
 
 class nsBig5Prober: public nsCharSetProber {
 public:
-  nsBig5Prober(void){mCodingSM = new nsCodingStateMachine(&Big5SMModel);
-                      Reset();}
+  nsBig5Prober(PRBool aIsPreferredLanguage)
+    :mIsPreferredLanguage(aIsPreferredLanguage) 
+  {mCodingSM = new nsCodingStateMachine(&Big5SMModel); 
+    Reset();}
   virtual ~nsBig5Prober(void){delete mCodingSM;}
   nsProbingState HandleData(const char* aBuf, PRUint32 aLen);
   const char* GetCharSetName() {return "Big5";}
   nsProbingState GetState(void) {return mState;}
   void      Reset(void);
   float     GetConfidence(void);
   void      SetOpion() {}
 
@@ -58,14 +60,15 @@ protected:
   void      GetDistribution(PRUint32 aCharLen, const char* aStr);
   
   nsCodingStateMachine* mCodingSM;
   nsProbingState mState;
 
   //Big5ContextAnalysis mContextAnalyser;
   Big5DistributionAnalysis mDistributionAnalyser;
   char mLastChar[2];
+  PRBool mIsPreferredLanguage;
 
 };
 
 
 #endif /* nsBig5Prober_h__ */
 

--- a/extensions/universalchardet/src/base/nsEUCJPProber.cpp
+++ b/extensions/universalchardet/src/base/nsEUCJPProber.cpp
@@ -86,14 +86,14 @@ nsProbingState nsEUCJPProber::HandleData
     if (mContextAnalyser.GotEnoughData() && GetConfidence() > SHORTCUT_THRESHOLD)
       mState = eFoundIt;
 
   return mState;
 }
 
 float nsEUCJPProber::GetConfidence(void)
 {
-  float contxtCf = mContextAnalyser.GetConfidence();
-  float distribCf = mDistributionAnalyser.GetConfidence();
+  float contxtCf = mContextAnalyser.GetConfidence(mIsPreferredLanguage);
+  float distribCf = mDistributionAnalyser.GetConfidence(mIsPreferredLanguage);
 
   return (contxtCf > distribCf ? contxtCf : distribCf);
 }
 

--- a/extensions/universalchardet/src/base/nsEUCJPProber.h
+++ b/extensions/universalchardet/src/base/nsEUCJPProber.h
@@ -45,31 +45,34 @@
 
 #include "nsCharSetProber.h"
 #include "nsCodingStateMachine.h"
 #include "JpCntx.h"
 #include "CharDistribution.h"
 
 class nsEUCJPProber: public nsCharSetProber {
 public:
-  nsEUCJPProber(void){mCodingSM = new nsCodingStateMachine(&EUCJPSMModel);
-                      Reset();}
+  nsEUCJPProber(PRBool aIsPreferredLanguage)
+    :mIsPreferredLanguage(aIsPreferredLanguage)
+  {mCodingSM = new nsCodingStateMachine(&EUCJPSMModel);
+    Reset();}
   virtual ~nsEUCJPProber(void){delete mCodingSM;}
   nsProbingState HandleData(const char* aBuf, PRUint32 aLen);
   const char* GetCharSetName() {return "EUC-JP";}
   nsProbingState GetState(void) {return mState;}
   void      Reset(void);
   float     GetConfidence(void);
   void      SetOpion() {}
 
 protected:
   nsCodingStateMachine* mCodingSM;
   nsProbingState mState;
 
   EUCJPContextAnalysis mContextAnalyser;
   EUCJPDistributionAnalysis mDistributionAnalyser;
 
   char mLastChar[2];
+  PRBool mIsPreferredLanguage;
 };
 
 
 #endif /* nsEUCJPProber_h__ */
 

--- a/extensions/universalchardet/src/base/nsEUCKRProber.cpp
+++ b/extensions/universalchardet/src/base/nsEUCKRProber.cpp
@@ -79,13 +79,13 @@ nsProbingState nsEUCKRProber::HandleData
 //    else
 //      mDistributionAnalyser.HandleData(aBuf, aLen);
 
   return mState;
 }
 
 float nsEUCKRProber::GetConfidence(void)
 {
-  float distribCf = mDistributionAnalyser.GetConfidence();
+  float distribCf = mDistributionAnalyser.GetConfidence(mIsPreferredLanguage);
 
   return (float)distribCf;
 }
 

--- a/extensions/universalchardet/src/base/nsEUCKRProber.h
+++ b/extensions/universalchardet/src/base/nsEUCKRProber.h
@@ -39,18 +39,21 @@
 #define nsEUCKRProber_h__
 
 #include "nsCharSetProber.h"
 #include "nsCodingStateMachine.h"
 #include "CharDistribution.h"
 
 class nsEUCKRProber: public nsCharSetProber {
 public:
-  nsEUCKRProber(void){mCodingSM = new nsCodingStateMachine(&EUCKRSMModel);
-                      Reset();}
+  nsEUCKRProber(PRBool aIsPreferredLanguage)
+    :mIsPreferredLanguage(aIsPreferredLanguage)
+  {mCodingSM = new nsCodingStateMachine(&EUCKRSMModel);
+    Reset();
+  }
   virtual ~nsEUCKRProber(void){delete mCodingSM;}
   nsProbingState HandleData(const char* aBuf, PRUint32 aLen);
   const char* GetCharSetName() {return "EUC-KR";}
   nsProbingState GetState(void) {return mState;}
   void      Reset(void);
   float     GetConfidence(void);
   void      SetOpion() {}
 
@@ -58,14 +61,15 @@ protected:
   void      GetDistribution(PRUint32 aCharLen, const char* aStr);
   
   nsCodingStateMachine* mCodingSM;
   nsProbingState mState;
 
   //EUCKRContextAnalysis mContextAnalyser;
   EUCKRDistributionAnalysis mDistributionAnalyser;
   char mLastChar[2];
+  PRBool mIsPreferredLanguage;
 
 };
 
 
 #endif /* nsEUCKRProber_h__ */
 

--- a/extensions/universalchardet/src/base/nsEUCTWProber.cpp
+++ b/extensions/universalchardet/src/base/nsEUCTWProber.cpp
@@ -79,13 +79,13 @@ nsProbingState nsEUCTWProber::HandleData
 //    else
 //      mDistributionAnalyser.HandleData(aBuf, aLen);
 
   return mState;
 }
 
 float nsEUCTWProber::GetConfidence(void)
 {
-  float distribCf = mDistributionAnalyser.GetConfidence();
+  float distribCf = mDistributionAnalyser.GetConfidence(mIsPreferredLanguage);
 
   return (float)distribCf;
 }
 

--- a/extensions/universalchardet/src/base/nsEUCTWProber.h
+++ b/extensions/universalchardet/src/base/nsEUCTWProber.h
@@ -39,18 +39,20 @@
 #define nsEUCTWProber_h__
 
 #include "nsCharSetProber.h"
 #include "nsCodingStateMachine.h"
 #include "CharDistribution.h"
 
 class nsEUCTWProber: public nsCharSetProber {
 public:
-  nsEUCTWProber(void){mCodingSM = new nsCodingStateMachine(&EUCTWSMModel);
-                      Reset();}
+  nsEUCTWProber(PRBool aIsPreferredLanguage)
+    :mIsPreferredLanguage(aIsPreferredLanguage)
+  {mCodingSM = new nsCodingStateMachine(&EUCTWSMModel);
+    Reset();}
   virtual ~nsEUCTWProber(void){delete mCodingSM;}
   nsProbingState HandleData(const char* aBuf, PRUint32 aLen);
   const char* GetCharSetName() {return "x-euc-tw";}
   nsProbingState GetState(void) {return mState;}
   void      Reset(void);
   float     GetConfidence(void);
   void      SetOpion() {}
 
@@ -58,14 +60,15 @@ protected:
   void      GetDistribution(PRUint32 aCharLen, const char* aStr);
   
   nsCodingStateMachine* mCodingSM;
   nsProbingState mState;
 
   //EUCTWContextAnalysis mContextAnalyser;
   EUCTWDistributionAnalysis mDistributionAnalyser;
   char mLastChar[2];
+  PRBool mIsPreferredLanguage;
 
 };
 
 
 #endif /* nsEUCTWProber_h__ */
 

--- a/extensions/universalchardet/src/base/nsGB2312Prober.cpp
+++ b/extensions/universalchardet/src/base/nsGB2312Prober.cpp
@@ -84,13 +84,13 @@ nsProbingState nsGB18030Prober::HandleDa
 //    else
 //      mDistributionAnalyser.HandleData(aBuf, aLen);
 
   return mState;
 }
 
 float nsGB18030Prober::GetConfidence(void)
 {
-  float distribCf = mDistributionAnalyser.GetConfidence();
+  float distribCf = mDistributionAnalyser.GetConfidence(mIsPreferredLanguage);
 
   return (float)distribCf;
 }
 

--- a/extensions/universalchardet/src/base/nsGB2312Prober.h
+++ b/extensions/universalchardet/src/base/nsGB2312Prober.h
@@ -41,18 +41,20 @@
 #include "nsCharSetProber.h"
 #include "nsCodingStateMachine.h"
 #include "CharDistribution.h"
 
 // We use gb18030 to replace gb2312, because 18030 is a superset. 
 
 class nsGB18030Prober: public nsCharSetProber {
 public:
-  nsGB18030Prober(void){mCodingSM = new nsCodingStateMachine(&GB18030SMModel);
-                      Reset();}
+  nsGB18030Prober(PRBool aIsPreferredLanguage)
+    :mIsPreferredLanguage(aIsPreferredLanguage)
+  {mCodingSM = new nsCodingStateMachine(&GB18030SMModel);
+    Reset();}
   virtual ~nsGB18030Prober(void){delete mCodingSM;}
   nsProbingState HandleData(const char* aBuf, PRUint32 aLen);
   const char* GetCharSetName() {return "gb18030";}
   nsProbingState GetState(void) {return mState;}
   void      Reset(void);
   float     GetConfidence(void);
   void      SetOpion() {}
 
@@ -60,14 +62,15 @@ protected:
   void      GetDistribution(PRUint32 aCharLen, const char* aStr);
   
   nsCodingStateMachine* mCodingSM;
   nsProbingState mState;
 
   //GB2312ContextAnalysis mContextAnalyser;
   GB2312DistributionAnalysis mDistributionAnalyser;
   char mLastChar[2];
+  PRBool mIsPreferredLanguage;
 
 };
 
 
 #endif /* nsGB2312Prober_h__ */
 

--- a/extensions/universalchardet/src/base/nsMBCSGroupProber.cpp
+++ b/extensions/universalchardet/src/base/nsMBCSGroupProber.cpp
@@ -58,27 +58,27 @@ const char *ProberName[] =
 nsMBCSGroupProber::nsMBCSGroupProber(PRUint32 aLanguageFilter)
 {
   for (PRUint32 i = 0; i < NUM_OF_PROBERS; i++)
     mProbers[i] = nsnull;
 
   mProbers[0] = new nsUTF8Prober();
   if (aLanguageFilter & NS_FILTER_JAPANESE) 
   {
-    mProbers[1] = new nsSJISProber();
-    mProbers[2] = new nsEUCJPProber();
+    mProbers[1] = new nsSJISProber(aLanguageFilter == NS_FILTER_JAPANESE);
+    mProbers[2] = new nsEUCJPProber(aLanguageFilter == NS_FILTER_JAPANESE);
   }
   if (aLanguageFilter & NS_FILTER_CHINESE_SIMPLIFIED)
-    mProbers[3] = new nsGB18030Prober();
+    mProbers[3] = new nsGB18030Prober(aLanguageFilter == NS_FILTER_CHINESE_SIMPLIFIED);
   if (aLanguageFilter & NS_FILTER_KOREAN)
-    mProbers[4] = new nsEUCKRProber();
+    mProbers[4] = new nsEUCKRProber(aLanguageFilter == NS_FILTER_KOREAN);
   if (aLanguageFilter & NS_FILTER_CHINESE_TRADITIONAL) 
   {
-    mProbers[5] = new nsBig5Prober();
-    mProbers[6] = new nsEUCTWProber();
+    mProbers[5] = new nsBig5Prober(aLanguageFilter == NS_FILTER_CHINESE_TRADITIONAL);
+    mProbers[6] = new nsEUCTWProber(aLanguageFilter == NS_FILTER_CHINESE_TRADITIONAL);
   }
   Reset();
 }
 
 nsMBCSGroupProber::~nsMBCSGroupProber()
 {
   for (PRUint32 i = 0; i < NUM_OF_PROBERS; i++)
   {

--- a/extensions/universalchardet/src/base/nsSJISProber.cpp
+++ b/extensions/universalchardet/src/base/nsSJISProber.cpp
@@ -85,14 +85,14 @@ nsProbingState nsSJISProber::HandleData(
     if (mContextAnalyser.GotEnoughData() && GetConfidence() > SHORTCUT_THRESHOLD)
       mState = eFoundIt;
 
   return mState;
 }
 
 float nsSJISProber::GetConfidence(void)
 {
-  float contxtCf = mContextAnalyser.GetConfidence();
-  float distribCf = mDistributionAnalyser.GetConfidence();
+  float contxtCf = mContextAnalyser.GetConfidence(mIsPreferredLanguage);
+  float distribCf = mDistributionAnalyser.GetConfidence(mIsPreferredLanguage);
 
   return (contxtCf > distribCf ? contxtCf : distribCf);
 }
 

--- a/extensions/universalchardet/src/base/nsSJISProber.h
+++ b/extensions/universalchardet/src/base/nsSJISProber.h
@@ -46,32 +46,35 @@
 #include "nsCharSetProber.h"
 #include "nsCodingStateMachine.h"
 #include "JpCntx.h"
 #include "CharDistribution.h"
 
 
 class nsSJISProber: public nsCharSetProber {
 public:
-  nsSJISProber(void){mCodingSM = new nsCodingStateMachine(&SJISSMModel);
-                      Reset();}
+  nsSJISProber(PRBool aIsPreferredLanguage)
+    :mIsPreferredLanguage(aIsPreferredLanguage)
+  {mCodingSM = new nsCodingStateMachine(&SJISSMModel);
+    Reset();}
   virtual ~nsSJISProber(void){delete mCodingSM;}
   nsProbingState HandleData(const char* aBuf, PRUint32 aLen);
   const char* GetCharSetName() {return "Shift_JIS";}
   nsProbingState GetState(void) {return mState;}
   void      Reset(void);
   float     GetConfidence(void);
   void      SetOpion() {}
 
 protected:
   nsCodingStateMachine* mCodingSM;
   nsProbingState mState;
 
   SJISContextAnalysis mContextAnalyser;
   SJISDistributionAnalysis mDistributionAnalyser;
 
   char mLastChar[2];
+  PRBool mIsPreferredLanguage;
 
 };
 
 
 #endif /* nsSJISProber_h__ */
 

--- a/extensions/universalchardet/tests/Makefile.in
+++ b/extensions/universalchardet/tests/Makefile.in
@@ -78,12 +78,15 @@ relativesrcdir = extensions/universalcha
 		bug306272_text.html \
 		test_bug306272.html \
 		bug421271_text.html \
 		test_bug421271.html \
 		bug426271_text-euc-jp.html \
 		test_bug426271-euc-jp.html \
 		bug426271_text-utf-8.html \
 		test_bug426271-utf-8.html \
+		bug431054_text.html \
+		test_bug431054.html \
+		test_bug431054-japanese.html \
 		$(NULL)
 
 libs:: $(_TEST_FILES)
 	$(INSTALL) $(foreach f,$^,"$f") $(DEPTH)/_tests/testing/mochitest/tests/$(relativesrcdir)

new file mode 100644
--- /dev/null
+++ b/extensions/universalchardet/tests/bug431054_text.html
@@ -0,0 +1,5 @@
+<html>
+<body>
+¥í¥°¥¤¥ó
+</body>
+</html>

--- a/extensions/universalchardet/tests/test_bug306272.html
+++ b/extensions/universalchardet/tests/test_bug306272.html
@@ -17,17 +17,16 @@ https://bugzilla.mozilla.org/show_bug.cg
 </div>
 <iframe id="testframe"></iframe>
 <pre id="test">
 <script class="testbody" type="text/javascript">
 /** Test for Bug 306272 **/
 CharsetDetectionTests("bug306272_text.html",
 		      "UTF-8",
 		      new Array("ja_parallel_state_machine",
-				"ko_parallel_state_machine",
 				"zh_parallel_state_machine",
 				"zhtw_parallel_state_machine",
 				"zhcn_parallel_state_machine",
 				"cjk_parallel_state_machine",
 				"universal_charset_detector"));
 </script>
 </pre>
 </body>

new file mode 100644
--- /dev/null
+++ b/extensions/universalchardet/tests/test_bug431054-japanese.html
@@ -0,0 +1,28 @@
+<!DOCTYPE HTML>
+<html>
+<!--
+https://bugzilla.mozilla.org/show_bug.cgi?id=431054
+-->
+<head>
+  <title>Test for Bug 431054</title>
+  <script type="text/javascript" src="/MochiKit/MochiKit.js"></script>
+  <script type="text/javascript" src="/tests/SimpleTest/SimpleTest.js"></script>
+  <script type="text/javascript" src="CharsetDetectionTests.js"></script>
+  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css" />
+</head>
+<body>
+<a target="_blank" href="https://bugzilla.mozilla.org/show_bug.cgi?id=426271">Mozilla Bug 431054</a>
+<p id="display"></p>
+<div id="content" style="display: none">  
+</div>
+<iframe id="testframe"></iframe>
+<pre id="test">
+<script class="testbody" type="text/javascript">
+/** Test for Bug 431054 **/
+CharsetDetectionTests("bug431054_text.html",
+		      "EUC-JP",
+		      new Array("ja_parallel_state_machine"));
+</script>
+</pre>
+</body>
+</html>

new file mode 100644
--- /dev/null
+++ b/extensions/universalchardet/tests/test_bug431054.html
@@ -0,0 +1,32 @@
+<!DOCTYPE HTML>
+<html>
+<!--
+https://bugzilla.mozilla.org/show_bug.cgi?id=431054
+-->
+<head>
+  <title>Test for Bug 431054</title>
+  <script type="text/javascript" src="/MochiKit/MochiKit.js"></script>
+  <script type="text/javascript" src="/tests/SimpleTest/SimpleTest.js"></script>
+  <script type="text/javascript" src="CharsetDetectionTests.js"></script>
+  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css" />
+</head>
+<body>
+<a target="_blank" href="https://bugzilla.mozilla.org/show_bug.cgi?id=426271">Mozilla Bug 431054</a>
+<p id="display"></p>
+<div id="content" style="display: none">  
+</div>
+<iframe id="testframe"></iframe>
+<pre id="test">
+<script class="testbody" type="text/javascript">
+/** Test for Bug 431054 **/
+CharsetDetectionTests("bug431054_text.html",
+		      "windows-1252",
+		      new Array("zhtw_parallel_state_machine",
+				"zhcn_parallel_state_machine",
+				"zh_parallel_state_machine",
+				"cjk_parallel_state_machine",
+				"universal_charset_detector"));
+</script>
+</pre>
+</body>
+</html>