diff --git a/modules/libpref/src/prefapi.c b/modules/libpref/src/prefapi.c
index 78cf9fd5152..1e9dc41bea5 100644
--- a/modules/libpref/src/prefapi.c
+++ b/modules/libpref/src/prefapi.c
@@ -607,6 +607,10 @@ PREF_EvaluateConfigScript(const char * js_buffer, size_t length,
             if (c == '\n')
                 break;
         }
+
+        /* Free up gSavedLine to avoid MLK. */
+        if (gSavedLine) 
+            free(gSavedLine);
         gSavedLine = malloc(i+1);
         if (!gSavedLine)
             return JS_FALSE;
diff --git a/modules/libpref/src/prefapi.cpp b/modules/libpref/src/prefapi.cpp
index 78cf9fd5152..1e9dc41bea5 100644
--- a/modules/libpref/src/prefapi.cpp
+++ b/modules/libpref/src/prefapi.cpp
@@ -607,6 +607,10 @@ PREF_EvaluateConfigScript(const char * js_buffer, size_t length,
             if (c == '\n')
                 break;
         }
+
+        /* Free up gSavedLine to avoid MLK. */
+        if (gSavedLine) 
+            free(gSavedLine);
         gSavedLine = malloc(i+1);
         if (!gSavedLine)
             return JS_FALSE;