--- a/gfx/thebes/gfxPlatformGtk.cpp	2010-04-19 18:02:04.000000000 +0000
+++ b/gfx/thebes/gfxPlatformGtk.cpp	2010-04-25 11:36:49.000000000 +0000
@@ -91,7 +91,12 @@
 #include FT_FREETYPE_H
 #endif
 
+#include "nsIPrefService.h"
+#include "nsIPrefBranch.h"
+#include "nsServiceManagerUtils.h"
+
 gfxFontconfigUtils *gfxPlatformGtk::sFontconfigUtils = nsnull;
+static PRBool gUseSystemVisualFormat = PR_FALSE;
 
 #ifndef MOZ_PANGO
 typedef nsDataHashtable<nsStringHashKey, nsRefPtr<FontFamily> > FontTable;
@@ -127,6 +132,16 @@
     gCodepointsWithNoFonts = new gfxSparseBitSet();
     UpdateFontList();
 #endif
+
+    nsCOMPtr<nsIPrefBranch> prefs = do_GetService(NS_PREFSERVICE_CONTRACTID);
+    if (!prefs)
+        return;
+
+    PRBool val = PR_FALSE;
+    nsresult rv;
+    rv = prefs->GetBoolPref("gfx.system.visual.format", &val);
+    if (NS_SUCCEEDED(rv))
+        gUseSystemVisualFormat = val;
 }
 
 gfxPlatformGtk::~gfxPlatformGtk()
@@ -202,8 +217,14 @@
         return nsnull;
 
     GdkPixmap* pixmap = nsnull;
-    XRenderPictFormat* xrenderFormat =
-        XRenderFindStandardFormat(display, xrenderFormatID);
+    XRenderPictFormat* xrenderFormat = nsnull;
+
+    if (xrenderFormatID == PictStandardRGB24 && gUseSystemVisualFormat) {
+        // Actually we want not strictly RGB24, but the fastest non-alpha
+        // format (XXX to be verified if it is actually safe)
+        xrenderFormat = XRenderFindVisualFormat(display, GDK_VISUAL_XVISUAL(gdk_visual_get_system()));
+    }
+    if (!xrenderFormat) xrenderFormat = XRenderFindStandardFormat(display, xrenderFormatID);
 
     if (xrenderFormat) {
         pixmap = gdk_pixmap_new(nsnull, size.width, size.height,