diff --git a/content/xbl/src/nsXBLProtoImpl.cpp b/content/xbl/src/nsXBLProtoImpl.cpp
index f3c7402c79de..3b34673cdb23 100644
--- a/content/xbl/src/nsXBLProtoImpl.cpp
+++ b/content/xbl/src/nsXBLProtoImpl.cpp
@@ -187,6 +187,12 @@ nsXBLProtoImpl::DestroyMembers(nsXBLProtoImplMember* aBrokenMember)
     }
     curr->Destroy(compiled);
   }
+
+  // Now clear out mMembers so we don't try to call Destroy() on them again
+  delete mMembers;
+  mMembers = nsnull;
+  mConstructor = nsnull;
+  mDestructor = nsnull;
 }
 
 nsresult
diff --git a/content/xbl/src/nsXBLProtoImpl.h b/content/xbl/src/nsXBLProtoImpl.h
index bb324ba871ec..10998ba342a9 100644
--- a/content/xbl/src/nsXBLProtoImpl.h
+++ b/content/xbl/src/nsXBLProtoImpl.h
@@ -84,11 +84,14 @@ protected:
   
 public:
   nsCString mClassName; // The name of the class. 
+
+protected:
   void* mClassObject;   // The class object for the binding. We'll use this to pre-compile properties 
                         // and methods for the binding.
 
   nsXBLProtoImplMember* mMembers; // The members of an implementation are chained in this singly-linked list.
   
+public:
   nsXBLProtoImplAnonymousMethod* mConstructor; // Our class constructor.
   nsXBLProtoImplAnonymousMethod* mDestructor;  // Our class destructor.
 };
diff --git a/content/xbl/src/nsXBLProtoImplMethod.cpp b/content/xbl/src/nsXBLProtoImplMethod.cpp
index cefb3b370822..28338cf612ea 100644
--- a/content/xbl/src/nsXBLProtoImplMethod.cpp
+++ b/content/xbl/src/nsXBLProtoImplMethod.cpp
@@ -55,6 +55,9 @@ MOZ_DECL_CTOR_COUNTER(nsXBLProtoImplMethod)
 nsXBLProtoImplMethod::nsXBLProtoImplMethod(const PRUnichar* aName) :
   nsXBLProtoImplMember(aName), 
   mUncompiledMethod(nsnull)
+#ifdef DEBUG
+  , mIsCompiled(PR_FALSE)
+#endif
 {
   MOZ_COUNT_CTOR(nsXBLProtoImplMethod);
 }
@@ -67,6 +70,8 @@ nsXBLProtoImplMethod::~nsXBLProtoImplMethod()
 void
 nsXBLProtoImplMethod::Destroy(PRBool aIsCompiled)
 {
+  NS_PRECONDITION(aIsCompiled == mIsCompiled,
+                  "Incorrect aIsCompiled in nsXBLProtoImplMethod::Destroy");
   if (aIsCompiled) {
     if (mJSMethodObject)
       RemoveJSGCRoot(&mJSMethodObject);
@@ -81,6 +86,8 @@ nsXBLProtoImplMethod::Destroy(PRBool aIsCompiled)
 void 
 nsXBLProtoImplMethod::AppendBodyText(const nsAString& aText)
 {
+  NS_PRECONDITION(!mIsCompiled,
+                  "Must not be compiled when accessing uncompiled method");
   if (!mUncompiledMethod) {
     mUncompiledMethod = new nsXBLUncompiledMethod();
     if (!mUncompiledMethod)
@@ -93,6 +100,8 @@ nsXBLProtoImplMethod::AppendBodyText(const nsAString& aText)
 void 
 nsXBLProtoImplMethod::AddParameter(const nsAString& aText)
 {
+  NS_PRECONDITION(!mIsCompiled,
+                  "Must not be compiled when accessing uncompiled method");
   if (!mUncompiledMethod) {
     mUncompiledMethod = new nsXBLUncompiledMethod();
     if (!mUncompiledMethod)
@@ -105,6 +114,8 @@ nsXBLProtoImplMethod::AddParameter(const nsAString& aText)
 void
 nsXBLProtoImplMethod::SetLineNumber(PRUint32 aLineNumber)
 {
+  NS_PRECONDITION(!mIsCompiled,
+                  "Must not be compiled when accessing uncompiled method");
   if (!mUncompiledMethod) {
     mUncompiledMethod = new nsXBLUncompiledMethod();
     if (!mUncompiledMethod)
@@ -121,6 +132,8 @@ nsXBLProtoImplMethod::InstallMember(nsIScriptContext* aContext,
                                     void* aTargetClassObject,
                                     const nsCString& aClassStr)
 {
+  NS_PRECONDITION(mIsCompiled,
+                  "Should not be installing an uncompiled method");
   JSContext* cx = (JSContext*) aContext->GetNativeContext();
   JSObject * scriptObject = (JSObject *) aScriptObject;
   NS_ASSERTION(scriptObject, "uh-oh, script Object should NOT be null or bad things will happen");
@@ -147,9 +160,16 @@ nsresult
 nsXBLProtoImplMethod::CompileMember(nsIScriptContext* aContext, const nsCString& aClassStr,
                                     void* aClassObject)
 {
-  if (!aClassObject)
-    return NS_OK; // Nothing to do.
+  NS_PRECONDITION(!mIsCompiled,
+                  "Trying to compile an already-compiled method");
+  NS_PRECONDITION(aClassObject,
+                  "Must have class object to compile");
 
+#ifdef DEBUG
+  // We have some "ok" early returns after which we consider ourselves compiled
+  mIsCompiled = PR_TRUE;
+#endif
+  
   // No parameters or body was supplied, so don't install method.
   if (!mUncompiledMethod)
     return NS_OK;
@@ -168,6 +188,12 @@ nsXBLProtoImplMethod::CompileMember(nsIScriptContext* aContext, const nsCString&
     return NS_OK;
   }
 
+#ifdef DEBUG
+  // OK, now we have some error early returns that mean we're not
+  // really compiled...
+  mIsCompiled = PR_FALSE;
+#endif
+
   // We have a method.
   // Allocate an array for our arguments.
   PRInt32 paramCount = mUncompiledMethod->GetParameterCount();
@@ -221,16 +247,25 @@ nsXBLProtoImplMethod::CompileMember(nsIScriptContext* aContext, const nsCString&
     // Root the compiled prototype script object.
     JSContext* cx = NS_REINTERPRET_CAST(JSContext*,
                                         aContext->GetNativeContext());
-    if (!cx) return NS_ERROR_UNEXPECTED;
-    AddJSGCRoot(&mJSMethodObject, "nsXBLProtoImplMethod::mJSMethodObject");
+    rv = cx ?
+      AddJSGCRoot(&mJSMethodObject, "nsXBLProtoImplMethod::mJSMethodObject") :
+      NS_ERROR_UNEXPECTED;
+    if (NS_FAILED(rv)) {
+      mJSMethodObject = nsnull;
+    }
   }
   
-  return NS_OK;
+#ifdef DEBUG
+  mIsCompiled = NS_SUCCEEDED(rv);
+#endif
+  return rv;
 }
 
 nsresult
 nsXBLProtoImplAnonymousMethod::Execute(nsIContent* aBoundElement)
 {
+  NS_PRECONDITION(mIsCompiled, "Can't execute uncompiled method");
+  
   if (!mJSMethodObject) {
     // Nothing to do here
     return NS_OK;
diff --git a/content/xbl/src/nsXBLProtoImplMethod.h b/content/xbl/src/nsXBLProtoImplMethod.h
index 2e5a03f3eeab..c689302977f2 100644
--- a/content/xbl/src/nsXBLProtoImplMethod.h
+++ b/content/xbl/src/nsXBLProtoImplMethod.h
@@ -138,6 +138,10 @@ protected:
     nsXBLUncompiledMethod* mUncompiledMethod; // An object that represents the method before being compiled.
     JSObject * mJSMethodObject;               // The JS object for the method (after compilation)
   };
+
+#ifdef DEBUG
+  PRBool mIsCompiled;
+#endif
 };
 
 class nsXBLProtoImplAnonymousMethod : public nsXBLProtoImplMethod {
diff --git a/content/xbl/src/nsXBLProtoImplProperty.cpp b/content/xbl/src/nsXBLProtoImplProperty.cpp
index 87c9916f32db..50adfe410fcc 100644
--- a/content/xbl/src/nsXBLProtoImplProperty.cpp
+++ b/content/xbl/src/nsXBLProtoImplProperty.cpp
@@ -56,6 +56,9 @@ nsXBLProtoImplProperty::nsXBLProtoImplProperty(const PRUnichar* aName,
   mGetterText(nsnull),
   mSetterText(nsnull),
   mJSAttributes(JSPROP_ENUMERATE)
+#ifdef DEBUG
+  , mIsCompiled(PR_FALSE)
+#endif
 {
   MOZ_COUNT_CTOR(nsXBLProtoImplProperty);
 
@@ -79,6 +82,8 @@ nsXBLProtoImplProperty::~nsXBLProtoImplProperty()
 void
 nsXBLProtoImplProperty::Destroy(PRBool aIsCompiled)
 {
+  NS_PRECONDITION(aIsCompiled == mIsCompiled,
+                  "Incorrect aIsCompiled in nsXBLProtoImplProperty::Destroy");
   if (aIsCompiled) {
     if (mJSGetterObject)
       RemoveJSGCRoot(&mJSGetterObject);
@@ -96,6 +101,8 @@ nsXBLProtoImplProperty::Destroy(PRBool aIsCompiled)
 void 
 nsXBLProtoImplProperty::AppendGetterText(const nsAString& aText)
 {
+  NS_PRECONDITION(!mIsCompiled,
+                  "Must not be compiled when accessing getter text");
   if (!mGetterText) {
     mGetterText = new nsXBLTextWithLineNumber();
     if (!mGetterText)
@@ -108,6 +115,8 @@ nsXBLProtoImplProperty::AppendGetterText(const nsAString& aText)
 void 
 nsXBLProtoImplProperty::AppendSetterText(const nsAString& aText)
 {
+  NS_PRECONDITION(!mIsCompiled,
+                  "Must not be compiled when accessing setter text");
   if (!mSetterText) {
     mSetterText = new nsXBLTextWithLineNumber();
     if (!mSetterText)
@@ -118,7 +127,10 @@ nsXBLProtoImplProperty::AppendSetterText(const nsAString& aText)
 }
 
 void
-nsXBLProtoImplProperty::SetGetterLineNumber(PRUint32 aLineNumber) {
+nsXBLProtoImplProperty::SetGetterLineNumber(PRUint32 aLineNumber)
+{
+  NS_PRECONDITION(!mIsCompiled,
+                  "Must not be compiled when accessing getter text");
   if (!mGetterText) {
     mGetterText = new nsXBLTextWithLineNumber();
     if (!mGetterText)
@@ -129,7 +141,10 @@ nsXBLProtoImplProperty::SetGetterLineNumber(PRUint32 aLineNumber) {
 }
 
 void
-nsXBLProtoImplProperty::SetSetterLineNumber(PRUint32 aLineNumber) {
+nsXBLProtoImplProperty::SetSetterLineNumber(PRUint32 aLineNumber)
+{
+  NS_PRECONDITION(!mIsCompiled,
+                  "Must not be compiled when accessing setter text");
   if (!mSetterText) {
     mSetterText = new nsXBLTextWithLineNumber();
     if (!mSetterText)
@@ -148,6 +163,8 @@ nsXBLProtoImplProperty::InstallMember(nsIScriptContext* aContext,
                                       void* aTargetClassObject,
                                       const nsCString& aClassStr)
 {
+  NS_PRECONDITION(mIsCompiled,
+                  "Should not be installing an uncompiled property");
   JSContext* cx = (JSContext*) aContext->GetNativeContext();
   JSObject * scriptObject = (JSObject *) aScriptObject;
   NS_ASSERTION(scriptObject, "uh-oh, script Object should NOT be null or bad things will happen");
@@ -183,8 +200,10 @@ nsresult
 nsXBLProtoImplProperty::CompileMember(nsIScriptContext* aContext, const nsCString& aClassStr,
                                       void* aClassObject)
 {
-  if (!aClassObject)
-    return NS_OK; // Nothing to do.
+  NS_PRECONDITION(!mIsCompiled,
+                  "Trying to compile an already-compiled property");
+  NS_PRECONDITION(aClassObject,
+                  "Must have class object to compile");
 
   if (!mName)
     return NS_ERROR_FAILURE; // Without a valid name, we can't install the member.
@@ -246,7 +265,15 @@ nsXBLProtoImplProperty::CompileMember(nsIScriptContext* aContext, const nsCStrin
     mJSGetterObject = nsnull;
   }
   
-  nsresult rvG=rv;
+  if (NS_FAILED(rv)) {
+    // We failed to compile our getter.  So either we've set it to null, or
+    // it's still set to the text object.  In either case, it's safe to return
+    // the error here, since then we'll be cleaned up as uncompiled and that
+    // will be ok.  Going on and compiling the setter and _then_ returning an
+    // error, on the other hand, will try to clean up a compiled setter as
+    // uncompiled and crash.
+    return rv;
+  }
 
   PRBool deletedSetter = PR_FALSE;
   if (mSetterText) {
@@ -292,6 +319,10 @@ nsXBLProtoImplProperty::CompileMember(nsIScriptContext* aContext, const nsCStrin
     delete mSetterText;
     mJSSetterObject = nsnull;
   }
+
+#ifdef DEBUG
+  mIsCompiled = NS_SUCCEEDED(rv);
+#endif
   
-  return NS_SUCCEEDED(rv) ? rvG : rv;
+  return rv;
 }
diff --git a/content/xbl/src/nsXBLProtoImplProperty.h b/content/xbl/src/nsXBLProtoImplProperty.h
index b6e4fa6e59d8..0b991335e60a 100644
--- a/content/xbl/src/nsXBLProtoImplProperty.h
+++ b/content/xbl/src/nsXBLProtoImplProperty.h
@@ -88,6 +88,10 @@ protected:
   };
   
   uintN mJSAttributes;          // A flag for all our JS properties (getter/setter/readonly/shared/enum)
+
+#ifdef DEBUG
+  PRBool mIsCompiled;
+#endif
 };
 
 #endif // nsXBLProtoImplProperty_h__