The Tor Browser / file revision

 CodeMirror.registerGlobalHelper("fold", "comment", function(mode) {

   return mode.blockCommentStart && mode.blockCommentEnd;

 }, function(cm, start) {

   var mode = cm.getModeAt(start), startToken = mode.blockCommentStart, endToken = mode.blockCommentEnd;

   if (!startToken || !endToken) return;

   var line = start.line, lineText = cm.getLine(line);

   var startCh;

   for (var at = start.ch, pass = 0;;) {

     var found = at <= 0 ? -1 : lineText.lastIndexOf(startToken, at - 1);

     if (found == -1) {

       if (pass == 1) return;

       pass = 1;

       at = lineText.length;

       continue;

     }

     if (pass == 1 && found < start.ch) return;

     if (/comment/.test(cm.getTokenTypeAt(CodeMirror.Pos(line, found + 1)))) {

       startCh = found + startToken.length;

       break;

     }

     at = found - 1;

   }

   var depth = 1, lastLine = cm.lastLine(), end, endCh;

   outer: for (var i = line; i <= lastLine; ++i) {

     var text = cm.getLine(i), pos = i == line ? startCh : 0;

     for (;;) {

       var nextOpen = text.indexOf(startToken, pos), nextClose = text.indexOf(endToken, pos);

       if (nextOpen < 0) nextOpen = text.length;

       if (nextClose < 0) nextClose = text.length;

       pos = Math.min(nextOpen, nextClose);

       if (pos == text.length) break;

       if (pos == nextOpen) ++depth;

       else if (!--depth) { end = i; endCh = pos; break outer; }

       ++pos;

     }

   }

   if (end == null || line == end && endCh == startCh) return;

   return {from: CodeMirror.Pos(line, startCh),

           to: CodeMirror.Pos(end, endCh)};

 });