diff --git a/dom/plugins/PluginLibrary.h b/dom/plugins/PluginLibrary.h
index 4e0ac4644e5..0923ecbc549 100644
--- a/dom/plugins/PluginLibrary.h
+++ b/dom/plugins/PluginLibrary.h
@@ -66,7 +66,7 @@ public:
   virtual nsresult NP_Initialize(NPNetscapeFuncs* bFuncs, NPError* error) = 0;
 #endif
   virtual nsresult NP_Shutdown(NPError* error) = 0;
-  virtual nsresult NP_GetMIMEDescription(char** mimeDesc) = 0;
+  virtual nsresult NP_GetMIMEDescription(const char** mimeDesc) = 0;
   virtual nsresult NP_GetValue(void *future, NPPVariable aVariable,
                                void *aValue, NPError* error) = 0;
 #if defined(XP_WIN) || defined(XP_MACOSX) || defined(XP_OS2)
diff --git a/dom/plugins/PluginModuleParent.cpp b/dom/plugins/PluginModuleParent.cpp
index 3992937edfc..b13f519aaec 100644
--- a/dom/plugins/PluginModuleParent.cpp
+++ b/dom/plugins/PluginModuleParent.cpp
@@ -647,11 +647,11 @@ PluginModuleParent::NP_Shutdown(NPError* error)
 }
 
 nsresult
-PluginModuleParent::NP_GetMIMEDescription(char** mimeDesc)
+PluginModuleParent::NP_GetMIMEDescription(const char** mimeDesc)
 {
     PLUGIN_LOG_DEBUG_METHOD;
 
-    *mimeDesc = (char*)"application/x-foobar";
+    *mimeDesc = "application/x-foobar";
     return NS_OK;
 }
 
diff --git a/dom/plugins/PluginModuleParent.h b/dom/plugins/PluginModuleParent.h
index 9bd3cb606ea..3462d35e222 100644
--- a/dom/plugins/PluginModuleParent.h
+++ b/dom/plugins/PluginModuleParent.h
@@ -200,7 +200,7 @@ private:
     virtual nsresult NP_Initialize(NPNetscapeFuncs* bFuncs, NPError* error);
 #endif
     virtual nsresult NP_Shutdown(NPError* error);
-    virtual nsresult NP_GetMIMEDescription(char** mimeDesc);
+    virtual nsresult NP_GetMIMEDescription(const char** mimeDesc);
     virtual nsresult NP_GetValue(void *future, NPPVariable aVariable,
                                  void *aValue, NPError* error);
 #if defined(XP_WIN) || defined(XP_MACOSX) || defined(XP_OS2)
diff --git a/dom/plugins/PluginPRLibrary.h b/dom/plugins/PluginPRLibrary.h
index 99ede9b6bbf..2ae704cc498 100644
--- a/dom/plugins/PluginPRLibrary.h
+++ b/dom/plugins/PluginPRLibrary.h
@@ -165,7 +165,7 @@ public:
         return NS_OK;
     }
 
-    virtual nsresult NP_GetMIMEDescription(char** mimeDesc) {
+    virtual nsresult NP_GetMIMEDescription(const char** mimeDesc) {
         if (mNP_GetMIMEDescription) {
             *mimeDesc = mNP_GetMIMEDescription();
         }
diff --git a/modules/plugin/base/src/nsNPAPIPlugin.cpp b/modules/plugin/base/src/nsNPAPIPlugin.cpp
index bcd90c38549..ecd6c910569 100644
--- a/modules/plugin/base/src/nsNPAPIPlugin.cpp
+++ b/modules/plugin/base/src/nsNPAPIPlugin.cpp
@@ -663,7 +663,7 @@ nsNPAPIPlugin::Shutdown(void)
 nsresult
 nsNPAPIPlugin::GetMIMEDescription(const char* *resultingDesc)
 {
-  nsresult gmdResult = fLibrary->NP_GetMIMEDescription((char**)resultingDesc);
+  nsresult gmdResult = fLibrary->NP_GetMIMEDescription(resultingDesc);
   if (gmdResult != NS_OK) {
     return gmdResult;
   }