Mozilla MathML support: Don't return invalid MathML markup if an elem…

…ent has no data-mathml attribute, is not a math tag but has ARIA role="math"; e.g. MathJax output.

source/NVDAObjects/IAccessible/mozilla.py

@@ -184,7 +184,9 @@ def _get_mathMl(self):
 			if not mathPres.getLanguageFromMath(attr) and self.language:
 				attr = mathPres.insertLanguageIntoMath(attr, self.language)
 			return attr
-		# Assume the content is MathML.
+		if self.IA2Attributes.get("tag") != "math":
+			# This isn't MathML.
+			raise LookupError
 		if self.language:
 			attrs = ' xml:lang="%s"' % self.language
 		else: