diff --git a/js/src/frontend/FullParseHandler.h b/js/src/frontend/FullParseHandler.h
index e26d6fb47..9674ce341 100644
--- a/js/src/frontend/FullParseHandler.h
+++ b/js/src/frontend/FullParseHandler.h
@@ -1018,6 +1018,14 @@ class FullParseHandler
         syntaxParser = nullptr;
     }
 
+    // TenFourFox issue 533, from M1263355
+    bool canSkipLazyInnerFunctions() {
+        return !!lazyOuterFunction_;
+    }
+    bool canSkipLazyClosedOverBindings() {
+        return !!lazyOuterFunction_;
+    }
+
     LazyScript* lazyOuterFunction() {
         return lazyOuterFunction_;
     }
diff --git a/js/src/frontend/Parser.cpp b/js/src/frontend/Parser.cpp
index ab0b945ee..ab3150833 100644
--- a/js/src/frontend/Parser.cpp
+++ b/js/src/frontend/Parser.cpp
@@ -1120,8 +1120,11 @@ Parser<FullParseHandler>::defineFunctionThis()
 
     // Also define a this-binding if direct eval is used, in derived class
     // constructors (JSOP_CHECKRETURN relies on it) or if there's a debugger
-    // statement.
+    // statement, or if this is a lazy script that has a this-binding
+    // (TenFourFox issue 533).
     if (pc->sc->hasDirectEval() ||
+        (handler.canSkipLazyClosedOverBindings() &&
+         pc->sc->asFunctionBox()->function()->lazyScript()->hasThisBinding()) ||
         pc->sc->asFunctionBox()->isDerivedClassConstructor() ||
         pc->sc->hasDebuggerStatement())
     {
@@ -2936,6 +2939,9 @@ Parser<SyntaxParseHandler>::finishFunctionDefinition(Node pn, FunctionBox* funbo
         lazy->setIsDerivedClassConstructor();
     if (funbox->needsHomeObject())
         lazy->setNeedsHomeObject();
+    // TenFourFox issue 533
+    if (funbox->hasThisBinding())
+        lazy->setHasThisBinding();
     PropagateTransitiveParseFlags(funbox, lazy);
 
     fun->initLazyScript(lazy);
diff --git a/js/src/jsscript.cpp b/js/src/jsscript.cpp
index c2a7afae2..011c9d34a 100644
--- a/js/src/jsscript.cpp
+++ b/js/src/jsscript.cpp
@@ -4282,6 +4282,7 @@ LazyScript::CreateRaw(ExclusiveContext* cx, HandleFunction fun,
     p.hasBeenCloned = false;
     p.treatAsRunOnce = false;
     p.isAsync = false;
+    p.hasThisBinding = false;
 
     size_t bytes = (p.numFreeVariables * sizeof(FreeVariable))
                  + (p.numInnerFunctions * sizeof(HeapPtrFunction));
@@ -4312,6 +4313,7 @@ LazyScript::CreateRaw(ExclusiveContext* cx, HandleFunction fun,
     };
 
     p.version = version;
+    p.hasThisBinding = false;
     p.numFreeVariables = numFreeVariables;
     p.isAsync = false;
     p.numInnerFunctions = numInnerFunctions;
diff --git a/js/src/jsscript.h b/js/src/jsscript.h
index 90eb07ed9..1a72c7464 100644
--- a/js/src/jsscript.h
+++ b/js/src/jsscript.h
@@ -2150,7 +2150,7 @@ class LazyScript : public gc::TenuredCell
     // instead of private to suppress -Wunused-private-field compiler warnings.
   protected:
 #if JS_BITS_PER_WORD == 32
-    uint32_t padding;
+    //uint32_t padding; // widened after TenFourFox issue 533
 #endif
   private:
 
@@ -2158,8 +2158,7 @@ class LazyScript : public gc::TenuredCell
         // Assorted bits that should really be in ScriptSourceObject.
         uint32_t version : 8;
 
-        uint32_t numFreeVariables : 23;
-        uint32_t isAsync: 1;
+        uint32_t numFreeVariables : 22;
         uint32_t numInnerFunctions : 20;
 
         uint32_t generatorKindBits : 2;
@@ -2167,6 +2166,8 @@ class LazyScript : public gc::TenuredCell
         // N.B. These are booleans but need to be uint32_t to pack correctly on MSVC.
         // If you add another boolean here, make sure to initialze it in
         // LazyScript::CreateRaw().
+        uint32_t hasThisBinding : 1;
+        uint32_t isAsync: 1;
         uint32_t strict : 1;
         uint32_t bindingsAccessedDynamically : 1;
         uint32_t hasDebuggerStatement : 1;
@@ -2368,6 +2369,13 @@ class LazyScript : public gc::TenuredCell
         p_.needsHomeObject = true;
     }
 
+    bool hasThisBinding() const {
+        return p_.hasThisBinding;
+    }
+    void setHasThisBinding() {
+        p_.hasThisBinding = true;
+    }
+
     const char* filename() const {
         return scriptSource()->filename();
     }