--- a/dom/base/nsDocument.cpp
+++ b/dom/base/nsDocument.cpp
@@ -1302,16 +1302,17 @@ nsIDocument::nsIDocument()
     // unless we get a window, and in that case the docshell value will get
     // &&-ed in, this is safe.
     mAllowDNSPrefetch(true),
     mIsBeingUsedAsImage(false),
     mHasLinksToUpdate(false),
     mFontFaceSetDirty(true),
     mGetUserFontSetCalled(false),
     mPostedFlushUserFontSet(false),
+    mBidiOptions(IBMBIDI_DEFAULT_BIDI_OPTIONS),
     mPartID(0),
     mDidFireDOMContentLoaded(true),
     mHasScrollLinkedEffect(false),
     mUserHasInteracted(false)
 {
   SetIsInDocument();
 
   PR_INIT_CLIST(&mDOMMediaQueryLists);

--- a/intl/unicharutil/util/nsBidiUtils.h
+++ b/intl/unicharutil/util/nsBidiUtils.h
@@ -157,22 +157,16 @@ typedef enum nsCharType nsCharType;
 //  If Pref values are to be changed
 //  in the XUL file of Prefs. the values
 //  Must be changed here too..
 //  ------------------
 //
 #define IBMBIDI_TEXTDIRECTION_STR       "bidi.direction"
 #define IBMBIDI_TEXTTYPE_STR            "bidi.texttype"
 #define IBMBIDI_NUMERAL_STR             "bidi.numeral"
-#define IBMBIDI_SUPPORTMODE_STR         "bidi.support"
-
-#define IBMBIDI_TEXTDIRECTION       1
-#define IBMBIDI_TEXTTYPE            2
-#define IBMBIDI_NUMERAL             4
-#define IBMBIDI_SUPPORTMODE         5
 
 //  ------------------
 //  Text Direction
 //  ------------------
 //  bidi.direction
 #define IBMBIDI_TEXTDIRECTION_LTR     1 //  1 = directionLTRBidi *
 #define IBMBIDI_TEXTDIRECTION_RTL     2 //  2 = directionRTLBidi
 //  ------------------
@@ -188,39 +182,29 @@ typedef enum nsCharType nsCharType;
 //  bidi.numeral
 #define IBMBIDI_NUMERAL_NOMINAL       0 //  0 = nominalnumeralBidi *
 #define IBMBIDI_NUMERAL_REGULAR       1 //  1 = regularcontextnumeralBidi
 #define IBMBIDI_NUMERAL_HINDICONTEXT  2 //  2 = hindicontextnumeralBidi
 #define IBMBIDI_NUMERAL_ARABIC        3 //  3 = arabicnumeralBidi
 #define IBMBIDI_NUMERAL_HINDI         4 //  4 = hindinumeralBidi
 #define IBMBIDI_NUMERAL_PERSIANCONTEXT 5 // 5 = persiancontextnumeralBidi
 #define IBMBIDI_NUMERAL_PERSIAN       6 //  6 = persiannumeralBidi
-//  ------------------
-//  Support Mode
-//  ------------------
-//  bidi.support
-#define IBMBIDI_SUPPORTMODE_MOZILLA     1 //  1 = mozillaBidisupport *
-#define IBMBIDI_SUPPORTMODE_OSBIDI      2 //  2 = OsBidisupport
-#define IBMBIDI_SUPPORTMODE_DISABLE     3 //  3 = disableBidisupport
 
 #define IBMBIDI_DEFAULT_BIDI_OPTIONS              \
         ((IBMBIDI_TEXTDIRECTION_LTR<<0)         | \
          (IBMBIDI_TEXTTYPE_CHARSET<<4)          | \
-         (IBMBIDI_NUMERAL_NOMINAL<<8)          | \
-         (IBMBIDI_SUPPORTMODE_MOZILLA<<12))
+         (IBMBIDI_NUMERAL_NOMINAL<<8))
 
 #define GET_BIDI_OPTION_DIRECTION(bo) (((bo)>>0) & 0x0000000F) /* 4 bits for DIRECTION */
 #define GET_BIDI_OPTION_TEXTTYPE(bo) (((bo)>>4) & 0x0000000F) /* 4 bits for TEXTTYPE */
 #define GET_BIDI_OPTION_NUMERAL(bo) (((bo)>>8) & 0x0000000F) /* 4 bits for NUMERAL */
-#define GET_BIDI_OPTION_SUPPORT(bo) (((bo)>>12) & 0x0000000F) /* 4 bits for SUPPORT */
 
 #define SET_BIDI_OPTION_DIRECTION(bo, dir) {(bo)=((bo) & 0xFFFFFFF0)|(((dir)& 0x0000000F)<<0);}
 #define SET_BIDI_OPTION_TEXTTYPE(bo, tt) {(bo)=((bo) & 0xFFFFFF0F)|(((tt)& 0x0000000F)<<4);}
 #define SET_BIDI_OPTION_NUMERAL(bo, num) {(bo)=((bo) & 0xFFFFF0FF)|(((num)& 0x0000000F)<<8);}
-#define SET_BIDI_OPTION_SUPPORT(bo, sup) {(bo)=((bo) & 0xFFFF0FFF)|(((sup)& 0x0000000F)<<12);}
 
 /* Constants related to the position of numerics in the codepage */
 #define START_HINDI_DIGITS              0x0660
 #define END_HINDI_DIGITS                0x0669
 #define START_ARABIC_DIGITS             0x0030
 #define END_ARABIC_DIGITS               0x0039
 #define START_FARSI_DIGITS              0x06f0
 #define END_FARSI_DIGITS                0x06f9

--- a/layout/base/nsPresContext.cpp
+++ b/layout/base/nsPresContext.cpp
@@ -598,21 +598,16 @@ nsPresContext::GetUserPreferences()
                         GET_BIDI_OPTION_TEXTTYPE(bidiOptions));
   SET_BIDI_OPTION_TEXTTYPE(bidiOptions, prefInt);
 
   prefInt =
     Preferences::GetInt(IBMBIDI_NUMERAL_STR,
                         GET_BIDI_OPTION_NUMERAL(bidiOptions));
   SET_BIDI_OPTION_NUMERAL(bidiOptions, prefInt);
 
-  prefInt =
-    Preferences::GetInt(IBMBIDI_SUPPORTMODE_STR,
-                        GET_BIDI_OPTION_SUPPORT(bidiOptions));
-  SET_BIDI_OPTION_SUPPORT(bidiOptions, prefInt);
-
   // We don't need to force reflow: either we are initializing a new
   // prescontext or we are being called from UpdateAfterPreferencesChanged()
   // which triggers a reflow anyway.
   SetBidi(bidiOptions, false);
 }
 
 void
 nsPresContext::InvalidatePaintedLayers()

--- a/modules/libpref/init/all.js
+++ b/modules/libpref/init/all.js
@@ -2411,23 +2411,16 @@ pref("bidi.texttype", 1);
 // 0 = nominalnumeralBidi *
 // 1 = regularcontextnumeralBidi
 // 2 = hindicontextnumeralBidi
 // 3 = arabicnumeralBidi
 // 4 = hindinumeralBidi
 // 5 = persiancontextnumeralBidi
 // 6 = persiannumeralBidi
 pref("bidi.numeral", 0);
-// ------------------
-//  Support Mode
-// ------------------
-// 1 = mozillaBidisupport *
-// 2 = OsBidisupport
-// 3 = disableBidisupport
-pref("bidi.support", 1);
 // Whether delete and backspace should immediately delete characters not
 // visually adjacent to the caret, or adjust the visual position of the caret
 // on the first keypress and delete the character on a second keypress
 pref("bidi.edit.delete_immediately", true);
 
 // Bidi caret movement style:
 // 0 = logical
 // 1 = visual