diff -Naur mozilla-1.9.1/xpcom/io/nsAppFileLocationProvider.cpp mozilla-1.9.1.tpg/xpcom/io/nsAppFileLocationProvider.cpp
--- mozilla-1.9.1/xpcom/io/nsAppFileLocationProvider.cpp	2009-07-15 15:36:07.000000000 +0000
+++ mozilla-1.9.1.tpg/xpcom/io/nsAppFileLocationProvider.cpp	2009-07-25 14:56:12.000000000 +0000
@@ -203,6 +203,14 @@
         if (NS_SUCCEEDED(rv))
             rv = localFile->AppendRelativeNativePath(PLUGINS_DIR_NAME);
     }
+    else if (nsCRT::strcmp(prop, "/usr/lib64/mozilla/plugins") == 0)
+    {
+        rv = NS_NewNativeLocalFile(nsDependentCString("/usr/lib64/mozilla/plugins"), PR_TRUE, getter_AddRefs(localFile));
+    }
+    else if (nsCRT::strcmp(prop, "/usr/lib/mozilla/plugins") == 0)
+    {
+        rv = NS_NewNativeLocalFile(nsDependentCString("/usr/lib/mozilla/plugins"), PR_TRUE, getter_AddRefs(localFile));
+    }
 #ifdef MOZ_WIDGET_COCOA
     else if (nsCRT::strcmp(prop, NS_MACOSX_USER_PLUGIN_DIR) == 0)
     {
@@ -593,7 +601,7 @@
         *_retval = new nsAppDirectoryEnumerator(this, keys);
 #else
 #ifdef XP_UNIX
-        static const char* keys[] = { nsnull, NS_USER_PLUGINS_DIR, NS_APP_PLUGINS_DIR, NS_SYSTEM_PLUGINS_DIR, nsnull };
+        static const char* keys[] = { nsnull, "/usr/lib64/mozilla/plugins", "/usr/lib/mozilla/plugins", NS_USER_PLUGINS_DIR, NS_APP_PLUGINS_DIR, nsnull };
 #else
         static const char* keys[] = { nsnull, NS_USER_PLUGINS_DIR, NS_APP_PLUGINS_DIR, nsnull };
 #endif