I just saw this on a MIX session recording, and I LOVE it
This adds in C# designtime behaviors into Javascript. What I mean by that is (from the JScript Editor Extensions page)
Brace Matching
Adds support for automatically highlighting the matching opening or closing brace to the one currently at the cursor. Supports matching parenthesis: (), square brackets: [], and curly braces: {}. Braces in strings, comments and regular expression literals are ignored.
Outlining / Cold-folding
Adds support for automatically creating outlining regions for JScript blocks. Blocks are detected via opening and closing curly braces. Braces in strings, comments and regular expression literals are ignored.
Current Word Highlighting
Adds support for highlighting all instances of the word currently at the cursor.