Some fonts don't have the nbsp character, so we spend time looking for an alternate font. Instead, just change the nbsp to a space; they render the same. Bug 238598, r+sr=dbaron.

gfx/src/gtk/nsFontMetricsXft.cpp

@@ -902,6 +902,13 @@ nsFontMetricsXft::CacheFontMetrics(void)
 nsFontXft *
 nsFontMetricsXft::FindFont(PRUint32 aChar)
 {
+    // If we have an NBSP character, we can treat it as a normal space.
+    // This helps because some fonts don't claim to support NBSP, and we waste
+    // time looking for a font that does.  The only difference is for
+    // line-breaking, and that has already been done for us in layout.
+
+    if (aChar == 0xa0)
+        aChar = ' ';
 
     // If mPattern is null, set up the base bits of it so we can
     // match.  If we need to match later we don't have to set it up