Removing usage of the obsolete xulrunner

--- lucidor.sh
+++ lucidor.sh
@@ -2,13 +2,11 @@
 
 DIR=lucidor
 
-if which xulrunner; then
-    xulrunner $DIR/application.ini "$@";
-elif which firefox; then
+if which firefox 2>/dev/null ; then
     firefox -app $DIR/application.ini "$@";
-elif which iceweasel; then
+elif which iceweasel 2>/dev/null ; then
     iceweasel -app $DIR/application.ini "$@";
-elif which abrowser; then
+elif which abrowser 2>/dev/null ; then
     abrowser -app $DIR/application.ini "$@";
 else
     echo "Could not find XULRunner runtime engine."