diff -up firefox-50.0/modules/libpref/prefapi.cpp.440908 firefox-50.0/modules/libpref/prefapi.cpp

--- firefox-50.0/modules/libpref/prefapi.cpp.440908	2016-10-31 21:15:26.000000000 +0100

+++ firefox-50.0/modules/libpref/prefapi.cpp	2016-11-10 10:32:48.796115692 +0100

@@ -997,8 +997,8 @@ void PREF_ReaderCallback(void       *clo

                          PrefValue   value,

                          PrefType    type,

                          bool        isDefault,

-                         bool        isStickyDefault)

-

+                         bool        isStickyDefault,

+                         bool        isLocked)

 {

     uint32_t flags = 0;

     if (isDefault) {

@@ -1010,4 +1010,6 @@ void PREF_ReaderCallback(void       *clo

         flags |= kPrefForceSet;

     }

     pref_HashPref(pref, value, type, flags);

+    if (isLocked)

+        PREF_LockPref(pref, true);

 }

diff -up firefox-50.0/modules/libpref/prefapi.h.440908 firefox-50.0/modules/libpref/prefapi.h

--- firefox-50.0/modules/libpref/prefapi.h.440908	2016-11-10 10:32:48.796115692 +0100

+++ firefox-50.0/modules/libpref/prefapi.h	2016-11-10 10:34:58.013159112 +0100

@@ -243,8 +243,8 @@ void PREF_ReaderCallback( void *closure,

                           PrefValue   value,

                           PrefType    type,

                           bool        isDefault,

-                          bool        isStickyDefault);

-

+                          bool        isStickyDefault,

+                          bool        isLocked);

 /*

  * Callback whenever we change a preference

diff -up firefox-50.0/modules/libpref/prefread.cpp.440908 firefox-50.0/modules/libpref/prefread.cpp

--- firefox-50.0/modules/libpref/prefread.cpp.440908	2016-09-05 22:12:58.000000000 +0200

+++ firefox-50.0/modules/libpref/prefread.cpp	2016-11-10 10:32:48.796115692 +0100

@@ -43,6 +43,7 @@ enum {

 #define BITS_PER_HEX_DIGIT      4

 static const char kUserPref[] = "user_pref";

+static const char kLockPref[] = "lockPref";

 static const char kPref[] = "pref";

 static const char kPrefSticky[] = "sticky_pref";

 static const char kTrue[] = "true";

@@ -146,7 +147,7 @@ pref_DoCallback(PrefParseState *ps)

         break;

     }

     (*ps->reader)(ps->closure, ps->lb, value, ps->vtype, ps->fdefault,

-                  ps->fstickydefault);

+                  ps->fstickydefault, ps->flock);

     return true;

 }

@@ -215,6 +216,7 @@ PREF_ParseBuf(PrefParseState *ps, const

                 ps->vtype = PrefType::Invalid;

                 ps->fdefault = false;

                 ps->fstickydefault = false;

+                ps->flock = false;

             }

             switch (c) {

             case '/':       /* begin comment block or line? */

@@ -225,11 +227,14 @@ PREF_ParseBuf(PrefParseState *ps, const

                 break;

             case 'u':       /* indicating user_pref */

             case 's':       /* indicating sticky_pref */

+            case 'l':       /* indicating lockPref */

             case 'p':       /* indicating pref */

                 if (c == 'u') {

                   ps->smatch = kUserPref;

                 } else if (c == 's') {

                   ps->smatch = kPrefSticky;

+                } else if (c == 'l') {

+                  ps->smatch = kLockPref;

                 } else {

                   ps->smatch = kPref;

                 }

@@ -277,8 +282,10 @@ PREF_ParseBuf(PrefParseState *ps, const

         /* name parsing */

         case PREF_PARSE_UNTIL_NAME:

             if (c == '\"' || c == '\'') {

-                ps->fdefault = (ps->smatch == kPref || ps->smatch == kPrefSticky);

+                ps->fdefault = (ps->smatch == kPref || ps->smatch == kPrefSticky

+                                || ps->smatch == kLockPref);

                 ps->fstickydefault = (ps->smatch == kPrefSticky);

+                ps->flock = (ps->smatch == kLockPref);

                 ps->quotechar = c;

                 ps->nextstate = PREF_PARSE_UNTIL_COMMA; /* return here when done */

                 state = PREF_PARSE_QUOTED_STRING;

diff -up firefox-50.0/modules/libpref/prefread.h.440908 firefox-50.0/modules/libpref/prefread.h

--- firefox-50.0/modules/libpref/prefread.h.440908	2016-09-05 22:12:58.000000000 +0200

+++ firefox-50.0/modules/libpref/prefread.h	2016-11-10 10:32:48.796115692 +0100

@@ -34,7 +34,8 @@ typedef void (*PrefReader)(void       *c

                            PrefValue   val,

                            PrefType    type,

                            bool        defPref,

-                           bool        stickyPref);

+                           bool        stickyPref,

+                           bool        lockPref);

 /**

  * Report any errors or warnings we encounter during parsing.

@@ -62,6 +63,7 @@ typedef struct PrefParseState {

     PrefType    vtype;      /* PREF_STRING,INT,BOOL          */

     bool        fdefault;   /* true if (default) pref        */

     bool        fstickydefault; /* true if (sticky) pref     */

+    bool        flock;      /* true if pref to be locked     */

 } PrefParseState;

 /**

@@ -90,7 +92,7 @@ void PREF_InitParseState(PrefParseState

  *

  * @param ps

  *        PrefParseState instance.

- */        

+ */

 void PREF_FinalizeParseState(PrefParseState *ps);

 /**