diff --git a/modules/libpr0n/decoders/png/nsPNGDecoder.cpp b/modules/libpr0n/decoders/png/nsPNGDecoder.cpp
index 0317041ee889..717d872072bd 100644
--- a/modules/libpr0n/decoders/png/nsPNGDecoder.cpp
+++ b/modules/libpr0n/decoders/png/nsPNGDecoder.cpp
@@ -207,6 +207,11 @@ info_callback(png_structp png_ptr, png_infop info_ptr)
   png_set_bgr(png_ptr);
 #endif
 
+#if defined(XP_MAC) || defined(XP_MACOSX)
+  // MacOS likes pixels padded to word boundaries
+  png_set_filler(png_ptr, 0, PNG_FILLER_BEFORE);
+#endif
+
   if (png_get_gAMA(png_ptr, info_ptr, &aGamma)) {
       if (aGamma < 0)
           aGamma = 0.45455;
@@ -301,9 +306,10 @@ info_callback(png_structp png_ptr, png_infop info_ptr)
   PRUint32 bpr, abpr;
   decoder->mFrame->GetImageBytesPerRow(&bpr);
   decoder->mFrame->GetAlphaBytesPerRow(&abpr);
-  decoder->colorLine = (PRUint8 *)nsMemory::Alloc(bpr);
-  if (channels > 3)
+  if (channels > 3) {
+    decoder->colorLine = (PRUint8 *)nsMemory::Alloc(bpr);
     decoder->alphaLine = (PRUint8 *)nsMemory::Alloc(abpr);
+  }
 
   if (interlace_type == PNG_INTERLACE_ADAM7) {
     decoder->interlacebuf = (PRUint8 *)nsMemory::Alloc(channels*width*height);
@@ -382,18 +388,7 @@ row_callback(png_structp png_ptr, png_bytep new_row,
     switch (format) {
     case gfxIFormats::RGB:
     case gfxIFormats::BGR:
-#if defined(XP_MAC) || defined(XP_MACOSX)
-        cptr = decoder->colorLine;
-        for (PRUint32 x=0; x<iwidth; x++) {
-          *cptr++ = 0;
-          *cptr++ = *line++;
-          *cptr++ = *line++;
-          *cptr++ = *line++;
-        }
-        decoder->mFrame->SetImageData(decoder->colorLine, bpr, row_num*bpr);
-#else
-        decoder->mFrame->SetImageData((PRUint8*)line, bpr, row_num*bpr);
-#endif
+      decoder->mFrame->SetImageData((PRUint8*)line, bpr, row_num*bpr);
       break;
     case gfxIFormats::RGB_A1:
     case gfxIFormats::BGR_A1:
@@ -444,26 +439,6 @@ row_callback(png_structp png_ptr, png_bytep new_row,
         decoder->mFrame->SetImageData(decoder->colorLine, bpr, row_num*bpr);
       }
       break;
-    case gfxIFormats::RGBA:
-    case gfxIFormats::BGRA:
-#if defined(XP_MAC) || defined(XP_MACOSX)
-      {
-        cptr = decoder->colorLine;
-        aptr = decoder->alphaLine;
-        for (PRUint32 x=0; x<iwidth; x++) {
-          *cptr++ = 0;
-          *cptr++ = *line++;
-          *cptr++ = *line++;
-          *cptr++ = *line++;
-          *aptr++ = *line++;
-        }
-        decoder->mFrame->SetAlphaData(decoder->alphaLine, abpr, row_num*abpr);
-        decoder->mFrame->SetImageData(decoder->colorLine, bpr, row_num*bpr);
-      }
-#else
-      decoder->mFrame->SetImageData(line, bpr, row_num*bpr);
-#endif
-      break;
     }
 
     nsRect r(0, row_num, width, 1);