--- a/layout/tools/reftest/reftest-content.js
+++ b/layout/tools/reftest/reftest-content.js
@@ -43,17 +43,17 @@ function clearTimeout(id) {
 }
 
 const XHTML_NS = "http://www.w3.org/1999/xhtml";
 
 const DEBUG_CONTRACTID = "@mozilla.org/xpcom/debug;1";
 const PRINTSETTINGS_CONTRACTID = "@mozilla.org/gfx/printsettings-service;1";
 
 // "<!--CLEAR-->"
-const BLANK_URL_FOR_CLEARING = "data:text/html,%3C%21%2D%2DCLEAR%2D%2D%3E";
+const BLANK_URL_FOR_CLEARING = "data:text/html;charset=UTF-8,%3C%21%2D%2DCLEAR%2D%2D%3E";
 
 var gBrowserIsRemote;
 var gHaveCanvasSnapshot = false;
 // Plugin layers can be updated asynchronously, so to make sure that all
 // layer surfaces have the right content, we need to listen for explicit
 // "MozPaintWait" and "MozPaintWaitFinished" events that signal when it's OK
 // to take snapshots. We cannot take a snapshot while the number of
 // "MozPaintWait" events fired exceeds the number of "MozPaintWaitFinished"

--- a/layout/tools/reftest/reftest.js
+++ b/layout/tools/reftest/reftest.js
@@ -42,17 +42,17 @@ var gTimeoutHook = null;
 var gRemote = false;
 var gIgnoreWindowSize = false;
 var gTotalChunks = 0;
 var gThisChunk = 0;
 var gContainingWindow = null;
 var gFilter = null;
 
 // "<!--CLEAR-->"
-const BLANK_URL_FOR_CLEARING = "data:text/html,%3C%21%2D%2DCLEAR%2D%2D%3E";
+const BLANK_URL_FOR_CLEARING = "data:text/html;charset=UTF-8,%3C%21%2D%2DCLEAR%2D%2D%3E";
 
 var gBrowser;
 // Are we testing web content loaded in a separate process?
 var gBrowserIsRemote;           // bool
 // Are we using <iframe mozbrowser>?
 var gBrowserIsIframe;           // bool
 var gBrowserMessageManager;
 var gCanvas1, gCanvas2;