diff --git a/gfx/layers/composite/ContentHost.cpp b/gfx/layers/composite/ContentHost.cpp
index 60ce1ff17d8..bab9855f0d7 100644
--- a/gfx/layers/composite/ContentHost.cpp
+++ b/gfx/layers/composite/ContentHost.cpp
@@ -219,13 +219,13 @@ ContentHostBase::Dump(FILE* aFile,
     fprintf(aFile, "<ul>");
   }
   if (mTextureHost) {
-    fprintf(aFile, aPrefix);
+    fprintf(aFile, "%s", aPrefix);
     fprintf(aFile, aDumpHtml ? "<li> <a href=" : "Front buffer: ");
     DumpTextureHost(aFile, mTextureHost);
     fprintf(aFile, aDumpHtml ? "> Front buffer </a></li> " : " ");
   }
   if (mTextureHostOnWhite) {
-    fprintf(aFile, aPrefix);
+    fprintf(aFile, "%s", aPrefix);
     fprintf(aFile, aDumpHtml ? "<li> <a href=" : "TextureHost on white: ");
     DumpTextureHost(aFile, mTextureHostOnWhite);
     fprintf(aFile, aDumpHtml ? "> Front buffer on white </a> </li> " : " ");
@@ -736,13 +736,13 @@ ContentHostDoubleBuffered::Dump(FILE* aFile,
     fprintf(aFile, "<ul>");
   }
   if (mBackHost) {
-    fprintf(aFile, aPrefix);
+    fprintf(aFile, "%s", aPrefix);
     fprintf(aFile, aDumpHtml ? "<li> <a href=" : "Back buffer: ");
     DumpTextureHost(aFile, mBackHost);
     fprintf(aFile, aDumpHtml ? " >Back buffer</a></li>" : " ");
   }
   if (mBackHostOnWhite) {
-    fprintf(aFile, aPrefix);
+    fprintf(aFile, "%s", aPrefix);
     fprintf(aFile, aDumpHtml ? "<li> <a href=" : "Back buffer on white: ");
     DumpTextureHost(aFile, mBackHostOnWhite);
     fprintf(aFile, aDumpHtml ? " >Back buffer on white</a> </li>" : " ");
diff --git a/gfx/layers/composite/ImageHost.cpp b/gfx/layers/composite/ImageHost.cpp
index 884f21e031e..eb479984445 100644
--- a/gfx/layers/composite/ImageHost.cpp
+++ b/gfx/layers/composite/ImageHost.cpp
@@ -189,7 +189,7 @@ ImageHostSingle::Dump(FILE* aFile,
     aFile = stderr;
   }
   if (mTextureHost) {
-    fprintf(aFile, aPrefix);
+    fprintf(aFile, "%s", aPrefix);
     fprintf(aFile, aDumpHtml ? "<ul><li>TextureHost: "
                              : "TextureHost: ");
     DumpTextureHost(aFile, mTextureHost);
diff --git a/gfx/layers/composite/TiledContentHost.cpp b/gfx/layers/composite/TiledContentHost.cpp
index 1a6815cff51..81159628911 100644
--- a/gfx/layers/composite/TiledContentHost.cpp
+++ b/gfx/layers/composite/TiledContentHost.cpp
@@ -327,7 +327,7 @@ TiledContentHost::Dump(FILE* aFile,
     fprintf(aFile, "<ul>");
   }
   for (;it != stop; ++it) {
-    fprintf(aFile, aPrefix);
+    fprintf(aFile, "%s", aPrefix);
     fprintf(aFile, aDumpHtml ? "<li> <a href=" : "Tile ");
     DumpTextureHost(aFile, it->mTextureHost);
     fprintf(aFile, aDumpHtml ? " >Tile</a></li>" : " ");